Sift together flour, cream of tartar and bicarb soda. Beat together eggs, sugar, milk, vanilla and cocoa (optional). Mix together wet and dry then pour into two round cake tins.
Bake in preheated oven until a knife inserted into the centre comes out clean. Allow to cool then place the two cakes on top of each other with a layer of your favourite jam and mock cream or icing. Dust with icing sugar to serve.