200g unsalted butter, 150g white chocolate, 300g light muscovado sugar, 3 large eggs, 200g plain flour, 1/4 tsp salt, 1 tsp vanilla extract, 75g raspberries, 75g blueberries
Heat oven to 180C/fan 160C. Butter and line a shallow rectangular tin approx 25cm x 22cm. Melt butter in a pan, then cook gently for about 5 mins until butter smells biscuity and sweet. Cool for 5 mins, then add half white chocolate and set aside for a couple of mins to melt. Stir until smooth. Whisk sugar and eggs together with electric whisk for about 2 mins until thick and pale. Tip in flour, salt, cooled chocolatey butter and vanilla, then fold in with metal spoon until even. Pour mixture into tin then scatter with rest of chocolate and raspberries and blueberries. Bake for 40-45 mins or until risen all over with a dark golden crust. Cool in the tin and then cut into squares.