Preheat oven to 350°F (175°C). Grease and line two 9-inch cake pans.
Beat eggs and sugar until pale and tripled in volume (5-7 minutes). Add vanilla.
Sift flour, baking powder, and salt in a separate bowl.
Gently fold dry ingredients into egg mixture without deflating.
Divide batter evenly and bake for 20-25 minutes or until a toothpick comes out clean.
Cool cakes in pans for 10 minutes, then transfer to wire racks.
Mix coffee, coffee liqueur, and sugar for the soak. Let cool.
Beat mascarpone until smooth. Whip heavy cream, powdered sugar, and vanilla until stiff peaks form.
Gently fold whipped cream into mascarpone mixture. Add coffee liqueur.
Slice each cake horizontally to make four layers.
Place the first cake layer on a stand and brush with coffee soak.
Spread mascarpone filling evenly. Dust with cocoa powder. Repeat for all layers.
Finish with mascarpone, cocoa powder, chocolate shavings, and berries.
Refrigerate for at least 4 hours (preferably overnight) before serving.