Set oven to 350F or Mark 4. Line a 7 inch square baking tin with buttered greaseproof paper. Put the butter, sugar and treacle together in a saucepan and heat gently until the fat melts. Sieve the flour and bicarbonate of soda into a bowl and add the oatmeal, sugar and spices. Add the melted treacle mixture, the beaten egg and the milk. Stir well until blended. Pour into the tin and bake for about 45 minutes. Cool in the tin for about 10 minutes then turn out on to a wire rack.
