1

First make the base. Preheat the oven to 180°C, fan 160°C, gas mark 4. Lightly whip the egg white until slightly foamy, then stir in the biscuit crumbs. Tip this mixture into a 20cm (8 inch) flan dish and spread out evenly over the base. Bake in the oven for about 5-6 minutes, until set. Remove and leave to cool slightly.

2

Meanwhile, make the filling. Blend the cornflour with the water in a small non-stick saucepan. Add the lemon zest and juice and bring to the boil, stirring constantly until the mixture thickens. Remove from the heat and add the sweetener. Cool slightly.

3

Stir the egg yolks into the lemon mixture, including the one left over from making the base. Pour this mixture over the base and return to the oven to bake for 10-12 minutes.

4

Whilst the filling is cooking, whisk the egg whites in a grease-free bowl until they hold their shape. Add the caster sugar and whisk again until stiff and glossy. Pile this mixture onto the set filling and return to the oven for 5-6 minutes, until browned.