Key Lime Pie Cake

Hello my dear friends! Continuing with the key lime recipes, today we have Key Lime Pie Cake!

So I’ve posted Key Lime Pie Macarons recipe this week, and Key Lime Brigadeiros (fudge truffles). And today we have this gorgeous cake here!

I still have one more key lime recipe to come! Stay tuned, I’ll come update this post later with a link for the next delicious key lime dessert I’m going to post. Hint: it’s macarons again!

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key lime pie cake slice

So let’s talk about today’s gorgeous cake!

This Key Lime Pie cake is filled with key lime pie filling (aka Key Lime Brigadeiro – brazilian condensed milk fudge), covered with Marshmallow frosting, coated in graham cracker crumbs! It’s just like a key lime pie, in form of a cake!

If you love key lime desserts, specially key lime pie, then this Key Lime Cake is for you!

key lime cake

Let’s start with the cake layers! They are Key Lime cake layers! With a delicious citrusy flavor.

Ps. feel free to use lime if you can’t find key lime, or if it’s not in season around you. I can usually only find key lime around July/August where I live, but lime would totally be a great substitute for this cake!

Here are our ingredients! Much easier if you gather them all before starting the recipe, just saying. Mise en place, friends!

ingredients to make key lime pie cake

Now let’s move on to the steps!

key lime cake steps
  1. Cream butter and oil until creamy and fluffy.
  2. Add sugar to the mixture and cream for another 2-3 minutes.
  3. Now, add eggs one at a time, and mix until combined.
  4. Add vanilla.
  5. Grab that lime zest and go ahead and add that too!
  6. After mixing to combine, add milk, and stir.
  7. Add half of the flour mixture and stir on the lowest setting of the mixer.
  8. After stirring, add the lime juice.
  9. Finally, add the remaining 1/2 of the dry ingredients in.
mixing cake batter with a spatula

I like to finish the cake stirring with a spatula, because it’s really important to never overmix a cake. And if you are using your mixer, chances of overmixing the cake are higher. Use a spatula if possible, because the cake will develop less gluten, and it will be fluffier, softer, more moist too!

baking key lime cake

Let’s talk a little bit about how to make the marshmallow frosting now.

How to make marshmallow frosting

Making marshmallow frosting is really easy! I mean it! This recipe only takes 5 ingredients and is super quick!

  • Egg whites
  • Granulated sugar
  • Salt
  • Cream of tartar
  • Vanilla extract
making marshmallow frosting

  1. Mix all ingredients except for the vanilla in a bowl over a double boiler.
  2. Whisk ingredients for a few minutes over barely simmering water, until they form a syrup and reach the temperature of 140F.
  3. Remove ingredients from the double boiler, and whip with an electric mixer for about 5 minutes on high speed.
  4. Add vanilla at the end. Make sure frosting is glossy, and has stiff peaks.

A few tips for the marshmallow frosting:

  • Marshmallow frosting is best if used on the day, as it may start to lose its structure and collapse after sitting for a while.
  • Make sure the syrup reaches 140F, because that will be the safe temperature to consume the eggs.
  • Don’t let any water get in the meringue, because any droplet of water may break the meringue, and it won’t achieve stiff peaks.
key lime pie cake

After the cake is baked, the fudge filling has cooled down to room temperature, and the frosting is ready, you can start to decorate the cake.

decorating key lime cake

Tips on how to assemble the Key Lime Pie Cake

  • Make sure the key lime pie filling is at room temperature. If it’s too cold, you won’t have an easy time spreading it on the cake. If it’s warm, it might melt the marshmallow frosting.
  • Pipe a ring of marshmallow frosting around the edges of the cake before putting the filling inside, to create a barrier so the filling will stay in the cake, and not come out to the sides.
  • You can use a piping bag to be able to spread the filling more evenly on the cake layers.
  • Use a simple syrup to make the cake layers moist and delicious. Read up below more about the simple syrup.

So, I like to make a simple syrup to brush on my cakes. And I added a little note at the end of the recipe explaining how to do that. It’s very simple. You grab equal parts of sugar and water, bring to a boil until the sugar melts. Then, let that syrup cool down all the way, and preferably chill it in the fridge until it gets thick. And brush this syrup on your cake as you decorate, before putting the filling on the cake.

Key Lime Pie Cake

A simple syrup brush will ensure you have a very moist and delicious cake.

For a cake the size of this Key Lime Pie Cake, I think about 1 cup of sugar and 1 cup of water syrup might be enough. I used to keep some simple syrup in my fridge when I used to make lots of layer cakes for orders and stuff. Simple syrup will keep in the fridge forever, and you can also use to sweeten cocktails, beverages, etc.

Another quick tip, if you are going to decorate the cake with those key lime rounds on the outside of the cake, make sure to let them drain a bit before sticking them to the side of the cake. Simply place the key lime rounds on top of a couple sheets of paper towel, and let them sit for 10 minutes or so.

key lime slices draining on a sheet of paper

And for the bottom of the cake, I used some graham cracker crumbs. I also used a torch to toast the marshmallow on the outside of the cake.

I topped the cake with key lime fudge truffles.

You can find the recipe for the key lime fudge truffles (brigadeiros) here. They’re made out of the same key lime pie filling you will put inside the cake, and you will most likely have a bit of leftover of filling, so you can roll it into balls, coat in sprinkles, or sparkling sugar to put on top of the cake.

key lime pie cake slice

If you want to see more Layer cake recipes, click here.

key lime pie cake

Here are some recipes you may like, if you like this Key Lime Pie Cake:

key lime pie cake slice

I hope you liked today’s recipe! Thank you so much for reading my blog and being a part of this! Happy baking!

Key Lime Pie Cake

Key Lime Pie Cake

Camila Hurst
This is a Key Lime Pie Cake, filled with key lime pie filling, frosted with Marshmallow Frosting, and coated in graham cracker crumbs!
4.25 from 4 votes
Prep Time 1 hour
Cook Time 30 minutes
Course Dessert
Cuisine American, brazilian
Servings 12 people
Calories 450 kcal


Key Lime Cake
  • 6 tablespoons  unsalted butter softened 3 oz, 85 grams
  • 2 tablespoons vegetable oil 29 ml
  • 3/4  cup  granulated sugar 5.29 oz, 150 grams
  • large eggs room temperature
  • teaspoons  vanilla extract
  • 2 tablespoons lime zest
  • 1 3/4  cup  all-purpose flour 7.8 oz, 221 grams
  • teaspoon  baking powder
  • 1/4 teaspoon baking soda
  • 1/4  teaspoon  salt
  • 1/2 cup milk 118 ml
  • 1/4 cup lime juice 59 ml
Key Lime Pie Filling
  • 2-14  oz  can of condensed milk
  • tablespoons  unsalted butter
  • 1-2  tablespoons  key lime zest
Marshmallow Frosting
  • egg whites
  • 3/4  cup  granulated sugar  150 grams, 5.29 oz.
  • 1/4  teaspoon  cream of tartar
  • 1/8  teaspoon  fine sea salt
  • teaspoon  vanilla extract
To decorate
  • Graham cracker crumbs
  • Key lime slices


  • Cake
  • Grease and flour 4 6” cake pans, or 2 8” cake pans.
  • Pre-heat oven to 350F.
  • Sift flour, baking powder, baking soda, and salt together. Set aside.
  • Cream butter and oil in the bowl of a stand mixer for 2 minutes, on medium speed. Gradually add sugar and cream for 3 minutes until mixture is fluffy and lighter in color.
  • Add eggs to the mixture, one at a time, mixing on medium speed. Scrape bowl and add vanilla. Mix on medium-low speed until incorporated.
  • Add lime zest and stir to combine.
  • Add milk to the bowl. Mix on low for 30 seconds. Add half of sifted flour mixture. Mix on low for 30-45 seconds until almost entirely incorporated.
  • Add lime juice and mix on low for 30 seconds. Add remaining flour and mix on low until incorporated.
  • Divide batter evenly between your cake pans.
  • Bake on pre-heated oven for about 20-25 minutes. Smaller cake pans will take less time to bake.
  • Remove cake from the oven when a toothpick comes out clean once inserted in the cake.
  • Let cake cool in the pan for 5 minutes and flip it over in a wire rack to let it cool completely before proceeding with frosting and filling.
Key Lime Pie filling
  • Place all ingredients in a small saucepan.
  • Bring to a boil over medium heat.
  • Keep stirring, non-stop, for 10-15 minutes while the mixture simmers. Don’t let the heat be too high, or it will burn the fudge. Also, don’t stop stirring, or that will also burn the fudge.
  • The fudge will be ready when it’s very thick and you can see the bottom of the pan easily as you stir with your spatula.
  • Tilt the pan over, and if the fudge comes off the bottom all at once, you can probably remove from the heat.
  • Place it in a heat proof bowl, let it cool down all the way.
  • Place room temperature filling in a piping bag.
Marshmallow Frosting
  • Mix all ingredients, except for the vanilla extract together in the bowl of a stand mixer.
  • Set the bowl over a pot of simmering water over medium heat.
  • Whisk mixture while it sits in the double boiler.
  • Keep whisking over simmering water until it reaches 140F.
  • That way the egg whites will be in a safe temperature to be consumed.
  • Move bowl to the mixer.
  • Whip with the whisk attachment for about 5 minutes on high speed.
  • Add vanilla and mix to combine.
To assemble
  • Place a cake layer on a cake plate.
  • Brush the cake with some simple syrup if desired. * (see notes)
  • Pipe some marshmallow frosting around the edges of the cake.
  • Pipe or spoon some of the key lime pie filling in the middle of the cake. Use a spatula to spread it evenly.
  • Place another cake layer on top. Repeat this process.
  • Frost the cake with an offset spatula, spreading the marshmallow frosting evenly all over the cake.
  • Grab some graham cracker crumbs with your hands, and attach them to the side of the cake.
  • Pipe some marshmallow frosting on top.
  • Use a torch to toast the marshmallow frosting if you want to.
  • This cake will keep nicely in the fridge for up to 3-4 days. Note that the marshmallow frosting may start collapsing after a day or two. Mine lasted 4 days, intact. But I’ve had it happen to me before that it collapsed.


*I like to soak my cakes with simple syrup. To make a simple syrup, just bring equal amounts of sugar and water to a boil until the sugar melts. And then wait for the syrup to cool down. Brush some syrup on top of the cake before filling and frosting it. For a cake this size I’d say making a syrup with 1 cup of sugar and 1 cup of water would be enough.
*Any leftover key lime pie filling will store nicely in the fridge for up to 2 weeks and in the freezer for a couple of months. Roll the leftover up into fudge balls, like here, and place them on top of the cake. Or eat it with a spoon.
Keyword cake

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  1. 5 stars
    I’m a total key lime fanatic, too! I love the idea of this cake, you’ve truly made a pie in a cake! It looks so good! I especially love that meringue-like frosting on top, just gorgeous! Pinning! I may want this as my birthday cake!

  2. Just double checking – if you use regular limes in the cake itself ? Is the only key lime in the filling ? Would it matter really if I used key limes in the cake? Looking forward to making this! Thanks.

    1. It really doesnt matter, either key limes or limes will work fine. Even lemon would work. The difference between key lime and lime will be a subtle taste difference 🙂

  3. 5 stars
    The perfect key lime flavor without being too strong & the BEST meringue icing :)) wish I could have a slice every day!

      1. Hello, thanks for sharing this recipe! quick question: if I’m using 2 8″ cake pans, do I need to cut them so that I have 4 layers?

  4. Hi Camila, the recipe looks delicious, my son loves key lime pie so we will try the cake. Couple of questions. Should I make the filling the same day as assembling the cake or can I make it a day ahead? Can I do some decorations/piping with this frosting?

    1. Hi there! The filling can be made a day before, just dont put it in the fridge because it will harden up and you wont be able to spread it. Leave it on the counter, it will be fine at room temperature for one to two days. and about the frosting, it’s marshmallow frosting, so you can definitely do some cute piping with it, but it’s a soft/elastic frosting, so it’s not as sturdy as buttercream.

      1. Thanks for your response, cake was good but didn’t raise much, next time I will use the 6 inch cake pans and will add more filling, filling is sooooo good!!!
        Thanks for the recipe 🙂

  5. 2 stars
    This was kind of a disaster for us. The cake layers were dry and didn’t rise at all so we had to double the recipe for it to be a normal-sized cake. The filling was yummy as was the icing but it didn’t stay in tact at all. We didn’t pipe the frosting, but I can’t imagine it piping well at all. Actually, the whole cake cracked and it gave us a good laugh. We’re pretty proficient bakers and I’m an avid cook but this one was a fail, unfortunately!

    1. You probably didnt whip the frosting enough, which is why it was runny. And the cake layers are supposed to be thin, which is why I stacked 4 of them, if they aren’t thin the cake is going to be too tall. I guarantee the recipe is correct, it was an issue with the execution.

  6. I look forward to trying this cake. I am confused about something. In the directions for the Key Lime Pie filling, it keeps referring to “fudge” . Is that what it is called or is that a typo? I just want to make sure. Thanks.

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