This written recipe is slightly different from my original video tutorial. Please follow these instructions!

Making the Cake Layers:

• Preheat the oven to 350F/177C. Line three, 8-inch (20-cm) round cake pans and grease the sides.
• Soften the butter at room temperature for about 30 minutes. Soften the mascarpone cheese for 10 to 15 minutes only! It can separate if too warm.
• Prepare the cake batter first. In a large mixing bowl, cream together softened butter, softened mascarpone cheese, sugar and vanilla on medium-high speed for 2 to 3 minutes, until creamy.
• In a separate bowl, whisk the egg whites on high speed for 4 to 5 minutes, until stiff peaks form. Add the egg whites to the batter and fold them in gently. Pour in the lukewam milk into the but do not mix; you will mix it in along with the flour.
• At this point, the batter will look like it's separated or curdled - do not panic! This happens because the milk fats in the butter are clumping together. The cake layers will turn out just fine.
• In a separate bowl, combine the dry ingredients: flour, baking powder and salt. Sift the dry ingredients into the batter, then whisk gently but thoroughly, mixing just until the flour is incorporated.
• In a small bowl, toss the mixed fruit with the cornstarch until the fruit is well coated. Add the fruit and lemon zest to the batter and fold in gently. Divide the cake batter evenly between the three pans.
• Bake in the preheated oven at 350F for 28 to 30 minutes, until a toothpick inserted into the comes out clean. Remove the cake layers from the oven, cool in the pans for 5 minutes, then cool completely on a wire rack.

Making the Mascarpone Frosting:

• Once layers are cooled, prepare the cream frosting. Place the mascarpone cheese (from the fridge) and vanilla into a mixing bowl and whisk on high speed for a minute, until the cheese is smooth and creamy.
• In a separate mixing bowl, prepare the whipped cream. Pour in the chilled cream into a mixer bowl and add the confectioner's sugar. Whisk on high speed for 3 to 4 minutes until stiff peaks form. Add the cheese mixture and the lemon zest and whisk for about 30 seconds to a minute, just until stiff peaks form. Keep the frosting refrigerated until you're ready to assemble the cake.

Assembling the Cake:

• To assemble the cake, first level the tops of the cake layers with a serrated knife, if needed. Spread a very generous amount of mascarpone frosting between each layer and add a mixutre berries and fruit between the layers.
• Apply a crumb coat of frosting on the outside of the cake, then refrigerate for 15 to 20 minutes. Smooth additional frosting over the top and sides, then garnish the cake with berries. The cake can be enjoyed right away, or refrigerated overnight.