For the Mixed Berry Puree:

1. Place the fresh berries, sugar, and salt in the bowl of a food processor and pulse until smooth. Strain the mixture through a fine mesh strainer to remove any seeds. Set aside.

For the Vanilla Cake Layers:

1. Preheat the oven to 350°F. Grease and flour four six-inch round cake pans (set aside two of the cake pans for the berry cakes).
2. Sift together the cake flour, baking powder, and salt. Set aside.
3. In the bowl of stand mixer, beat the butter for 2 minutes or until fluffy and pale yellow. Add the sugar and continue to beat for another few minutes.
4. Add the egg yolks, one at a time, mixing well after each addition. Whisk in the vanilla.
5. Add the flour mixture in two batches, alternating with the milk, being sure to mix until the dry ingredients are just incorporated. Fold in the sprinkles by hand.
6. Divide the batter evenly between two of the cake pans. Bake for 25-30 minutes, or until a toothpick inserted in the center of the cakes comes out clean. Cool in the pans for 10-15 minutes before removing them from the pans. Allow them to finish cooling on wire racks.

For the Mixed Berry Cake Layers:

1. Sift together the cake flour, baking powder, and salt. Set aside.
2. In the bowl of stand mixer, beat the butter for 2 minutes or until fluffy and pale yellow. Add the sugar and continue to beat for another 3- minutes.
3. Add the egg yolks, one at a time, mixing well after each addition. Whisk in the vanilla and the berry puree.
4. Add the flour mixture in two batches, alternating with the milk, being sure to mix until the dry ingredients are just incorporated. Fold in the sprinkles by hand.
5. Divide the batter evenly between the two remaining cake pans. Bake for 25-30 minutes, or until a toothpick inserted in the center of the cakes comes out clean. Cool in the pans for 10-15 minutes before removing them from the pans. Allow them to finish cooling on wire racks.

For the Berry Filling:

1. While the cakes are baking/cooling, beat the cream cheese and butter together in the stand mixer. Beat until fluffy and smooth. Gradually add the powdered sugar, beating it in on low speed. Whisk in the berry puree and beat until combined. Add a little more powdered sugar, as needed, to thicken the mixture. Beat until it is smooth and creamy. Transfer to a bowl and set aside. Wipe out the mixer bowl.

For the Vanilla Buttercream:

1. Place the egg whites and sugar in the bowl of the stand mixer and beat until combined. Fill a medium saucepan with an inch or two of water and place it over medium-high heat. Once the water comes to a simmer, place the mixing bowl on top of the pot to create a double boiler (the bottom of the bowl should not touch the water).
2. Whisking almost constantly, heat the egg whites and sugar until a candy thermometer reads 160°F. Carefully transfer the bowl to the stand mixer and beat on high speed for 8-10 minutes, or until stiff peaks form.
3. Swap the whisk attachment out for the paddle attachment and add the butter, a few tablespoons at a time, to the mixture. Do the same with the cream cheese. Beat until the mixture is silky smooth, about 5 minutes. Beat in the vanilla. Fold in the sprinkles until incorporated.

To Assemble:

1. Once the cakes have cooled completely, arrange one of the vanilla cake layers on a cake board/plate and place on a rotating cake stand (a cake stand is not necessary but it does make the frosting/decorating a lot easier).
2. Spread ⅓ of the berry filling on the cake, smoothing it out in an even layer with an offset spatula.
3. Top the vanilla cake with one of the berry cakes. Repeat with the berry filling. Repeat with the remaining cake layers/filling.
4. Using a clean offset spatula, begin frosting the cake with the vanilla buttercream by dolloping it on the top layer of the assembled layer cake and gently working a thin layer down the sides. Don’t worry too much about this first layer of frosting being too neat; it is the crumb coat and will be covered up by the final layer of frosting.
5. Carefully transfer the frosted cake to the fridge and allow it to set for 10-15 minutes.
6. Remove the chilled cake from the fridge and apply another layer of the frosting, smoothing it out as you go.
7. If desired, place any leftover buttercream in a piping bag and pipe any decorative border you see fit. Decorate with fresh berries and/or sprinkles. I went with a more simplistic approach and decorated with extra sprinkles only. Totally your call.
8. Store the cake in the fridge for up to four days. Allow it to come to room temperature about 15 minutes before you plan on serving it. Serve with additional sprinkles and/or fresh berries.

NOTES:

1. As someone who does not consider herself a seasoned baker, especially when it comes to fancy layer cakes, I found this easier to make and assemble in stages. I baked the cakes and made the fillings on one day and assembled everything the following day. You could easily spread this out over a few days, as needed, as long as you keep your unfrosted cake layers well wrapped in the fridge.