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 combined.
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 in the dry ingredients, lemon zest, and vanilla extract. Add melted butter and milk, mixing until just combined. Avoid overmixing.
05 - Divide batter evenly between prepared pans. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean.
06 - Let cakes cool in pans for 10 minutes, then turn out onto wire racks to cool completely.
07 - In a small saucepan, heat water and sugar over medium heat until sugar dissolves completely. Remove from heat, cool slightly, then stir in limoncello.
08 - 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.
09 - Slice each cake in half horizontally for four thin layers. Place first layer on a serving plate, brush generously with limoncello syrup, and spread a layer of mascarpone filling. Repeat with remaining layers, finishing with mascarpone frosting on top and sides.
10 - Decorate with lemon slices, zest, white chocolate curls, or edible flowers as desired. Refrigerate for at least 1 hour before serving for optimal flavor and texture.