Lemon tiramisu gateau

For the sponge:

1. Preheat the oven to 180 degrees, or 160 fan. Grease and line two 20 x 20cm square baking tins with parchment paper.

2. In a large bowl, whisk the eggs and sugar together for about five minutes until pale and voluminous — the mixture should have tripled in size. Gently fold in the self-raising flour in thirds.

3. In a small bowl, whisk the cornflour with 50ml of boiling water and add to the cake batter. The addition of cornflour gives the cake a light crumb.

4. Divide the mixture between the two tins and bake in the preheated oven for 25 minutes until golden and well-risen, or until a skewer inserted into the centre comes out clean.

5. Remove from the oven, leave to cool in the tins for 10 minutes, then turn out on to a wire rack and cool completely.

6. Once cold, transfer the sponges to the fridge for an hour before slicing each one in half horizontally. Chilling the sponges makes them easier to cut. Trim off any uneven edges and set aside.

For the syrup:

1. Put the limoncello (or lemon juice, if using) into a medium saucepan with the sugar and water and bring to a boil. Whisk to ensure the sugar has dissolved, then set aside to cool.

For the filling:

1. Whisk the egg yolks and sugar together in a large bowl until pale, about five minutes.

2. Beat the mascarpone to loosen slightly, then gently fold into the egg mix.

3. Fold in the lemon curd, then set aside until ready to assemble.

To assemble:

1. Line a 20 x 20cm square tin with two sheets of parchment paper or cling film.

2. Place one sponge square on the bottom and brush liberally with lemon syrup. Spread one third of the mascarpone mix on top.

3. Repeat with the second sponge, more syrup and the next third of mascarpone. Top with the third sponge, syrup and remaining mascarpone. Brush one side of the last sponge with syrup, then place the soaked side facing down. Chill the gateau for at least three hours.

4. When ready to serve, cut the cake into 10 rectangular slices. Pipe whipped cream on top of each slice and garnish with lemon zest.