Preheat the oven to 350F/177C. Line two, 8-inch (20-cm) cake pans with parchment paper and leave the sides ungreased.
Prepare the sponge cake first. Place the eggs, sugar and vanilla into a stand mixer bowl and whisk on high speed for 7 to 10 minutes, until the eggs are fluffy, voluminous and pale white in color. If using a hand mixer, this process will take up to 15 minutes. Combine the flour and baking powder, then sift into the egg mixture in thirds. Fold gently but thoroughly after each addition, mixing from the bottom of the mixing bowl.
Divide the cake batter evenly between the two pans and level the batter with an off-set spatula. Bake the cake layers for 20 to 22 minutes, until they’re a rich, golden color on top. Remove them immediately from the oven and run a knife or spatula along the edge of the pan to release the cake from the pan. Invert the cake layers onto a cooling rack, remove the parchment paper and then cool completely.
Mascarpone Whipped Cream Frosting:
While the cake layers are cooling, prepare the mascarpone frosting. Place the softened cheese into a large mixing bowl, add the vanilla, optional sweetened condensed milk and confectioner’s sugar. Beat on medium speed for a couple minutes, until the cheese is smooth and creamy.
Next, pour in the chilled heavy cream and whisk on slow speed first, then gradually move to high speed. Whisk for 3 to 4 minutes, until the frosting forms stiff peaks. If not assembling the cake right away, keep the frosting refrigerated.
Tres Leches Mixture:
For the tres leches mixture, combine the sweetened condensed milk, evaporated milk and whole milk in a large measuring cup. Whisk the milks together until uniform, about 1 minute.
Wash the berries and dry them on paper towels. Slice the strawberries into thin slices and cut blackberries in half if they’re too large.
Assembling the Berry Tres Leches Cake:
To assemble the cake, first ensure that the cake layers are completely cooled. Using a long, serrated knife, split each cake layer in half, creating 4 cake layers total. Place the first cake layer onto a cake stand and soak it generously with the prepared tres leches mixture using a spoon. Watch my video recipe to see how it’s done.
Next, add a generous amount of the prepared frosting (app. 1 ½ cups) onto the cake layer and spread it evenly to the edges with an off-set spatula. Top the frosting with mixed berries, pressing them very lightly into the frosting. Add the next cake layer and repeat the same process.
For the final cake layer, first soak the sponge cake with the tres leches mixture, then invert the cake layer onto the top. Add the remaining frosting on top and garnish with more berries and flowers, if desired.
Refrigerate the cake for at least 2 to 3 hours before enjoying. If making ahead of time, keep the sides of the cake wrapped with plastic wrap. Alternatively, prepare 1 ½ portions of the frosting recipe and frost the sides of the cake as well. This is a great option if you need the cake to stand for a couple days.