Preheat the oven to 350°F (180°C). Grease and flour an 8-9 inch cake pan.

In a bowl, combine flour, baking powder, and lemon zest.

In another bowl, beat eggs and sugar until light and fluffy.

Add melted butter, lemon juice, and optional limoncello to the egg mixture.

Gently fold the dry ingredients into the wet mixture, being careful not to overmix.

Pour batter into the prepared pan and bake for 30-35 minutes or until a toothpick inserted comes out clean.

Allow the cake to cool completely.

To make the filling, whip mascarpone and heavy cream with sugar and lemon juice until smooth.

Slice the cooled cake horizontally into two layers.

Spread the lemon cream filling evenly between the layers, then cover the top and sides of the cake with the remaining cream.

Chill the cake before serving for the best texture and flavor.