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 to 7 minutes.
04 - Gently fold in the flour mixture, lemon zest, and vanilla extract using a spatula, being careful not to deflate the batter.
05 - Add the melted butter and milk, mixing gently until just combined. Avoid overmixing to maintain the light texture.
06 - Divide batter evenly between prepared pans. Bake for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean.
07 - Let cakes cool in pans for 10 minutes, then carefully turn out onto wire racks to cool completely before assembly.
08 - In a small saucepan, heat water and sugar over medium heat, stirring until sugar completely dissolves. Remove from heat, allow to cool slightly, then stir in limoncello.
09 - In a chilled bowl, whip heavy cream until soft peaks form. In a separate bowl, whisk together mascarpone cheese, powdered sugar, lemon zest, and vanilla until smooth. Gently fold whipped cream into the mascarpone mixture until fully incorporated.
10 - Slice each cake layer horizontally in half to create four thin layers. Place first layer on a serving plate, brush generously with limoncello syrup, and spread an even layer of mascarpone filling. Repeat with remaining layers, finishing with mascarpone 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 and the cake to set properly.