1. Line the base and sides of an 18cm/7 inch square cake tin with greased baking parchment. Preheat the oven to 180C/160Cfan/gas 2.
2. Sift the flour, salt, all spice, ginger and bicarbonate of soda into a bowl. Add oatmeal and toss in well. Make a hollow in the centre.
3. Measure the Lyle’s Black Treacle, fat, Tate & Lyle Fairtrade sugar and milk into a pan and stir over a low heat until dissolved. Pour into the hollow with the egg and stir briskly until well blended.
4. Spoon the mixture into the prepared tin and bake for 1 – 1¼ hours until cooked through. A cocktail stick, when pushed gently into the centre, should come out clean. Cool until lukewarm, in tin, then turn out onto a wire rack.
5. Store in an airtight container, without removing paper, and leave 1 week before cutting.