01 - Preheat the oven to 350°F. Grease and line two 8-inch round cake pans with parchment paper.
02 - In a medium bowl, whisk together flour, baking powder, and salt until well blended.
03 - In a large bowl, beat eggs and sugar with an electric mixer on high speed until pale and tripled in volume, approximately 5–7 minutes.
04 - Gently fold the dry ingredients, lemon zest, and vanilla extract into the egg mixture using a spatula.
05 - Pour in melted butter and milk, folding gently until just combined. Avoid overmixing to maintain sponge texture.
06 - Divide batter evenly between prepared pans. Bake for 25–30 minutes until a toothpick inserted into the center comes out clean.
07 - Allow cakes to cool in pans for 10 minutes, then turn out onto wire racks to cool completely before assembly.
08 - In a small saucepan, heat water and sugar over medium heat until sugar dissolves completely. Remove from heat, let cool slightly, then stir in limoncello.
09 - In a chilled bowl, whip heavy cream to soft peaks. In another bowl, whisk mascarpone, powdered sugar, lemon zest, and vanilla until smooth. Gently fold whipped cream into mascarpone mixture until combined.
10 - Slice each cake horizontally in half for four thin layers. Place first layer on serving plate, brush generously with limoncello syrup, and spread with mascarpone filling. Repeat with remaining layers, finishing with frosting on top and sides.
11 - Garnish with lemon slices, zest, white chocolate curls, or edible flowers as desired. Refrigerate for at least 1 hour before serving to allow flavors to meld.