You will need 2 layers of sponge cake. You can either bake them one at a time or make a thicker cake and cut it into two. I bake each layer separately as I find it difficult to cut them evenly.
If you also choose to bake the two layers separately, start by mixing together a half measure of the batter ingredients. Mix on low speed at first and gradually increase the speed until you have a smooth mixture.
Preheat the oven to 180°C/356°F and line a baking sheet with parchment paper. I used a 36x24 cm (14x10 inch) sheet.
Pour the mixture onto the sheet and bake for 10-12 minutes or until firm.
Repeat with the second layer. Let them cool.
While they are cooling, prepare the cream.
In a bowl, mix the whipping cream, mascarpone, sugar, and vanilla until you get a stiff cream. Be sure to use mascarpone and whipping cream that have been refrigerated for at least 2-3 hours.
You can now assemble the cake. Spread all the cream on the first layer and cover with the second layer. Then place a plate, tray or a chopping board on top to gently press the cake together.
Refrigerate for at least 2-3 hours before slicing.