Vanilla buttermilk cake

1. Preheat the oven to 329°F / 165°C and line 3 6 inches / 15 cm diameter cake pans with parchment paper. (If you only have one pan, bake in 3 batches). 
2. In a large bowl, mix and sift together the dry ingredients, cake flour, baking powder, baking soda, and salt, then set aside.
3. In the mixing bowl of your stand mixer fitted with the whisk attachment, whip the softened butter with the sugar on medium-high speed for 3-5 minutes, until the mixture whitens and is creamy.
4. Reduce speed to medium-low and add the vanilla extract and egg, one by one, until fully incorporated.
5. Then continue on medium-high speed for about 5 minutes, until the mixture is voluminous.
6. Add the flour mixture and buttermilk alternately and in batches, using a flexible spatula just until the mixture is smooth and homogeneous.
7. Divide the mixture into 3 parts and divide between the prepared pans.
8. Bake for about 30 minutes, until golden and puffed on top. ( dip a toothpick or knife blade into the center of each cake to check that the center is baked, it should come out clean and with no liquid batter, otherwise extend the baking time by 5 minutes). 
9. Leave your cakes to cool in their pans for a few minutes before carefully removing them from the pans and placing them on a wire rack to cool. 

Mascarpone frosting

1. Place the cold mascarpone cheese, cold heavy cream, powdered sugar and vanilla extract in a large bowl.
2. Using an electric mixer, beat at medium speed for about 3 minutes until thick and creamy.
3. Keep in a cool place until ready to assemble. 

Assemble the cake

1. Using a cake leveler or a large saw knife, cut out the bumps in your 3 layers of cake.
2. Place the first cake layer on a cake plate set on a rotating cake tray. 
3. Fill the inside of the cake with mascarpone frosting, smooth with an angled spatula, place a few pieces of red fruit and cover with a bit of frosting.
4. Place a second layer of cake and repeat until you reach the last layer of cake.
5. If desired, apply a very thin layer of mascarpone frosting to the outside, then decorate the top with fresh berries.
6. Place the semi-naked cake in the fridge for 1 hour before serving.