Pre-heat the oven to 350ºF. Grease and line 3 8” cake pans with parchment paper.

In a bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In a large bowl, or in the bowl of a stand mixer, add the butter, oil, and sugar. Beat the ingredients together for two minutes, until the mixture is fluffy and light in color. If using a stand mixer, use the paddle attachment, or you can just use a hand mixer.

Add the eggs, one at a time, mixing one egg completely until incorporated before adding the next one.

Remember to scrape the bowl in between mixing.

Add the vanilla and mix to combine.

Add one third of the buttermilk to the bowl with the batter, mix on low to combine.

Next, add one third of the dry ingredient mixture. Mix on low speed.

Add another third of the buttermilk and mix.

Follow by another third of the flour mixture, mix to combine.

Add the remaining buttermilk, and mix. Finish with the remaining flour, add it to the bowl and mix on low.

You can finish by folding with a spatula, to avoid over mixing the batter.

Spread about 1/2 to 1 cup of batter on the bottom of each prepared cake pan, enough to cover the bottom and form a layer that’s about 3/4” thick. We place this layer of batter without blueberries on the bottom of the cake pan to prevent the blueberries from sinking.

To the remaining batter, add the blueberries and mix to combine.

Divide the batter between the prepared cake pans.

Bake in the pre-heated oven for about 30 minutes, until a toothpick inserted into the cake comes off clean.

Remove the cakes from the oven. After 10 minutes, flip the cakes onto a cooling rack or plate. Let the cake layers cool down completely.

If you aren’t assembling the cake on the same day, wrap each completely cooled down cake layer in plastic wrap, and place in the freezer until ready to assemble.

Place the blueberries, the sugar, and the lemon juice in a medium saucepan. Cook the blueberries over medium heat, stirring every so often, for about 10 minutes.

If the mixture is drying and sticking to the bottom of the pan, add one tablespoon of water, or more as needed.

Mix the cornstarch and water together until the cornstarch has dissolved.

Once the blueberries have softened and the mixture is thick and syrupy, add the dissolved cornstarch to the pan and immediately mix with a spatula. Cook for 2 minutes, stirring, until the sauce is thick.

Remove the sauce from the heat, and pour into a bowl. Cover with plastic wrap and let it cool down. Place it in the fridge until it’s time to use to fill the cake.

Place the blueberries in a blender. Blend until the blueberries becomes a puree, you should have about 1/2 cup of blueberry puree.

Pour the pureed blueberries in a medium saucepan, place over medium heat.

Bring to a simmer, and stir often.

Cook the puree until it reduces to 1/4 cup.

Once you have 1/4 cup, pour in a bowl and cover with plastic wrap directly on the surface of the puree so it doesn’t form a crust. Let the puree cool down completely. You can make it ahead and place in the fridge overnight.

Beat the butter in the bowl of a mixer for 30 seconds. Add the cream cheese and beat for another 30 seconds on medium-speed.

Add half of the powdered sugar, mix on low until combined. Raise the speed and beat on medium speed for just a few seconds.

Add the blueberry puree and mix on low.

Add the remaining powdered sugar, mix on low, and then raise the speed to medium-high, and beat for one minute.

If the frosting is too runny, add a bit more powdered sugar to make it thicker.

To assemble the cake, place a cake layer on a cake plate.

Spread a thin layer of the Blueberry Cream Cheese Frosting on top of the cake.

Place some of the Blueberry Cream Cheese Frosting in a piping bag fitted with a large round tip.

Pipe a ring of frosting around the edges of the cake.

Spread a layer of blueberry jam inside the ring of frosting.

Top with another cake layer.

Repeat the process by spreading a layer of frosting on the cake, then piping a ring of frosting around the edges, and filling the center with jam.

Top with the final cake layer.

Spread a thin amount of frosting on top of the cake and on the sides. Use an offset spatula, or a cake scraper to smooth out the frosting. This is called crumb coating, it helps seal the crumbs in, and makes it easier to smooth out the final coating of frosting.

Place the cake in the fridge until this layer of frosting has chilled, about 20 to 30 minutes.

Remove the cake from the fridge and spread the remaining frosting on top of the cake and on the sides.

Use the cake scraper to smooth out the frosting by placing it on the side of the cake, and keeping it steady as you spin the turntable around.

Smooth out the top of the cake using an offset spatula, swiping it over the edges of the cake gently towards you.

Decorate the cake with fresh blueberries and mint leaves if desired.

Store the leftover cake slices in the fridge, in an air-tight container.

If freezing the cake, wrap it in plastic and place in air-tight container, and remove the fresh blueberries.