Cinnamon Sponge

¼ lb. butter, ½ lb. sugar, ½ lb. flour, 3 eggs, 1 teaspoonful soda, 2 teaspoonfuls cream of tartar, 1 tablespoonful cinnamon, ½ cupful milk. Cream butter and sugar, then add eggs, beat all together. Sift soda, cream of tartar and cinnamon with flour. Bake in sandwich tins for about half an hour.
Filling: 1 tablespoonful of butter and 3 of castor sugar. Beat together to a cream and spread between the cakes when cold.