50g unsalted butter, softened
100g caster sugar
finely grated zest and juice of 1 lemon
2 eggs, separated
30g plain flour
Preheat the oven to 180ºC.
Cream together the butter, sugar and lemon zest until pale and fluffy. Stir in the egg yolks.
Sift the flour into the mixture and stir until smooth, then add the milk little by little. Stir in the lemon juice (don't worry if it looks split, it's meant to do that).
In a clean glass or metal bowl whisk your egg whites until stiff, then gently fold them into the mixture using a metal spoon until no lumps of egg white remain.
Pour the mixture into a baking dish, making sure to put your mixing bowl as close to the dish as possible as you pour so that you don't lose any air bubbles.
Bake for about 45 minutes until golden brown and crispy on top, it should still have a good wobble to it. Serve straight from the oven. You can eat it on it's own or with cream for a bit of extra decadence.