Preheat your oven to 350°F (175°C). Grease two 8-inch round cake pans and line the bottoms with parchment paper.

In a medium-sized mixing bowl, whisk together the all-purpose flour and baking powder until well combined.

In a separate mixing bowl, use an electric mixer to beat the egg whites until soft peaks form, about 2–3 minutes. Set aside.

In another large mixing bowl, beat the egg yolks with granulated sugar until pale and creamy, about 3–5 minutes. Fold in the lemon zest, lemon juice, and limoncello.

Gently fold the flour mixture into the yolk mixture, then fold in the egg whites in increments to maintain airiness.

Divide the batter between the prepared pans and bake for about 22–25 minutes, or until golden brown. Cool in the pans before transferring to wire racks.

Prepare the limoncello syrup by combining equal parts water and granulated sugar in a small saucepan. Bring to boil until sugar dissolves, then stir in limoncello.

Soak the top of each cooled cake layer with limoncello syrup using a pastry brush.

Beat the mascarpone cheese until smooth, then gradually add heavy cream, powdered sugar, and vanilla extract. Beat until fluffy.

Assemble the cake by spreading mascarpone frosting between layers and around the sides.

Chill the assembled cake in the refrigerator for at least 4 hours before serving.

Garnish with lemon zest curls or powdered sugar before serving.