Potato Sponge Cake with Walnuts

• 11 oz (310 g) potatoes, cooked and puréed
• 6 eggs

While the puréed potatoes are cooling, start to prepare the cake. Separate the eggs, beat the yolks with the sugar until the consistency is silky. Add the lemon rind, the flour, the cinnamon and lastly the potatoes. Then add the walnuts to the mixture. Whip the egg whites until stiff and fold them in gently.

Have ready a cake tin, well-oiled and lined with greaseproof paper. I use a nar