Preheat your oven to 180 °C (350 °F). Grease and line a 20 cm (8-inch) round cake pan with parchment paper.

Separate the egg whites and yolks. In a large bowl, beat the egg whites with a pinch of salt until soft peaks form. Gradually add half the sugar and continue beating until glossy and stiff.

In another bowl, beat the egg yolks with the remaining sugar and vanilla until pale and creamy.

Gently fold the egg yolk mixture into the beaten whites. Sift flour and baking powder over the top and fold carefully to maintain the airiness.

Pour the batter into the prepared pan and bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean. Allow the sponge to cool completely.

In a bowl, whip the chilled cream until soft peaks form. Add mascarpone, powdered sugar, and lemon zest (if using). Beat until smooth and fluffy.

Slice the cooled sponge cake in half horizontally. Spread the mascarpone filling evenly between the layers.

Place the top sponge layer back on, dust with powdered sugar, and decorate with fresh berries.

Chill for at least 1 hour before slicing to allow the filling to set slightly.