Make the Cake
Prep
Preheat oven to 350°F (175°C). Grease and line two 8-inch round cake pans with parchment paper.
Cream butter and sugar
Beat butter and sugar until light and fluffy, about 2–3 minutes.
Add eggs and vanilla
Add eggs one at a time, mixing well after each. Mix in vanilla extract.
Combine dry ingredients
In a separate bowl, whisk flour, baking powder, and salt.
Mix batter
Add dry ingredients to the wet mixture, alternating with milk. Mix just until combined.
Bake
Divide batter evenly between pans. Bake 25–30 minutes, until a toothpick inserted comes out clean.
Cool
Cool in pans for 10 minutes, then transfer to wire racks to cool completely.
Make the Chantilly Cream
Beat mascarpone (or cream cheese) until smooth.
Add powdered sugar and vanilla; mix until combined.
Slowly pour in cold heavy cream and whip until soft, fluffy peaks form.
Assemble the Cake
Place one cake layer on a serving plate.
Spread an even layer of chantilly cream on top.
Add a layer of mixed berries (pat dry first).
Place the second cake layer on top.
Frost the top and sides lightly and decorate with remaining berries.