Preheat oven to 180C Fan and lightly spray a baking tin of about 12”x9” / 30x22.5cm size with low fat cooking spray and line the base with greaseproof paper. Leave enough greaseproof paper hanging over the edge of the tin so you can use it to lift the sponge base out later.

Break the eggs into a separate bowl and lightly whisk these together before adding them to the rest of the mixture.

Beat the mixture firmly with a wooden spoon or use a stand mixer paddle on lowest speed to mix all of the ingredients together.

Scrape all of the ingredients from the mixing bowl into the tin. Smooth the top flat.

Bake for about 20 minutes. Once the mixture has risen and turned a golden colour use a wooden skewer to check that the middle is cooked. (Skewer should come out clean from the mixture).

Remove from oven. Allow to cool for 10 minutes but not go cold then remove from tin, using the greaseproof paper, to a wire rack.

Whilst still warm, spread the peanut butter all over the sponge, spreading evenly to the edges. Then place the peanut butter covered sponge back into the tin and pop in fridge for about an hour or so to allow the cake to fully cool.

Melt the chocolate in a glass bowl over a saucepan of gently simmering water and then spread it evenly over the peanut butter sponge layer, leaving the layer still in the tin. Again place in fridge to allow chocolate to harden for about 2 hours.

Run a sharp knife around the edge of the chocolate so you can lift the whole tray bake out of the tin and slice into 15 equal slices.