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Key Lime Pie Cake

Key Lime Pie Cake

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


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


  1. Cake
  2. Grease and flour 4 6” cake pans, or 2 8” cake pans.
  3. Pre-heat oven to 350F.
  4. Sift flour, baking powder, baking soda, and salt together. Set aside.
  5. 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.

  6. 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.
  7. Add lime zest and stir to combine.
  8. 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.
  9. Add lime juice and mix on low for 30 seconds. Add remaining flour and mix on low until incorporated.
  10. Divide batter evenly between your cake pans.
  11. Bake on pre-heated oven for about 20-25 minutes. Smaller cake pans will take less time to bake.
  12. Remove cake from the oven when a toothpick comes out clean once inserted in the cake.
  13. 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

  1. Place all ingredients in a small saucepan.
  2. Bring to a boil over medium heat.
  3. 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.
  4. 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.
  5. Tilt the pan over, and if the fudge comes off the bottom all at once, you can probably remove from the heat.
  6. Place it in a heat proof bowl, let it cool down all the way.
  7. Place room temperature filling in a piping bag.

Marshmallow Frosting

  1. Mix all ingredients, except for the vanilla extract together in the bowl of a stand mixer.
  2. Set the bowl over a pot of simmering water over medium heat.
  3. Whisk mixture while it sits in the double boiler.
  4. Keep whisking over simmering water until it reaches 140F.
  5. That way the egg whites will be in a safe temperature to be consumed.
  6. Move bowl to the mixer.
  7. Whip with the whisk attachment for about 5 minutes on high speed.
  8. Add vanilla and mix to combine.

To assemble

  1. Place a cake layer on a cake plate.
  2. Brush the cake with some simple syrup if desired. * (see notes)
  3. Pipe some marshmallow frosting around the edges of the cake.
  4. Pipe or spoon some of the key lime pie filling in the middle of the cake. Use a spatula to spread it evenly.
  5. Place another cake layer on top. Repeat this process.
  6. Frost the cake with an offset spatula, spreading the marshmallow frosting evenly all over the cake.
  7. Grab some graham cracker crumbs with your hands, and attach them to the side of the cake.
  8. Pipe some marshmallow frosting on top.
  9. Use a torch to toast the marshmallow frosting if you want to.


  1. 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.

Recipe Notes

*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.

Nutrition Facts
Key Lime Pie Cake
Amount Per Serving
Calories 450
* Percent Daily Values are based on a 2000 calorie diet.