Well grease and line a deep roasting tin, 10 inches by 13 inches. Place all the dry ingredients into a large mixing bowl. Gently heat the treacle and butter together in a saucepan until melted and pour into the dry mixture.
Stir well, add the beaten egg and stir again.
Warm the milk, add it to the mixture and beat well.
Pour into the tin and bake for 1 to 1 1/2 huors until firm. Leave in the tin for 1/2 hour, then turn out onto a wire rack.
Keep for 48 hours, then cut into squares to serve.