Blackberry Sponge Slices

Preheat the oven to 180°C (160°C fan) | 350F | gas 4. Grease and line a 2 lb straight-sided loaf tin with greaseproof paper.

Pulse the shortbread in a food processor with the melted butter until you have an even mixture that resembles fine breadcrumbs.

Pack the mixture into the base and sides of the tin and arrange the blackberries on top in an even layer.

Beat together the flour, sugar, margarine, eggs and yoghurt in a large mixing bowl using an electric beater until smooth. Spoon on top of the blackberries and spread evenly.

Bake for 20-25 minutes until a cake tester comes out clean. Remove from the oven and let the cake cool before attempting to turn out.

Prepare the puree by heating together the blueberries and the sugar in a small saucepan set over a medium heat, stirring until soft.

Pass the mixture through a fine sieve and collect the puree in a bowl underneath.