It is delicious. And very easy to make.
100g melted butter150g sugar
2 egg whites
50g tapioca flour (or potato flour)
150g plain flour
2 tsp baking powder
1 tsp vanilla essence
2 tbsp milk
Heat the oven to 180C. Grease the tin and flour it.
Whisk the melted butter and sugar until fluffy. Add the eggs, one at a time, and continue whisking. Zest the lemons and add the zest to the mixture, and then add the vanilla essence; stir together well.
Whisk the egg whites until firm and set aside. Mix together the plain flour, the potato flour and the baking powder, and sift into the egg mixture and beat together. Add the milk to create a runnier texture.
Using a metal spoon, fold in the beaten egg whites until they are well mixed in. Pour the mixture into the tin. Bake in the oven 25 minutes. When cooked, turn out the cake onto a rack. Dust the top with icing sugar.
If you can, leave it to cool before eating, with an espresso of course (though it goes just as well with tea in the afternoon). Serve with whipped cream or mascarpone and a spoonful of tart gooseberry compote.