Heat the oven to 375°. Sift the flour into a bowl and add the lemon rind. Cream the butter and sugar together and gradually add the eggs. Add the lemon essence and little milk (about 1 tbl) if required.

Pour into a greased and floured tin and bake for 1 to 1 1/4 hours. Put a slice of citron peel on top of the cake as soon as it is set.