“Melting white chocolate can be tricky. When it is in the bowl over a pan of just simmering water, don’t stir it or it may well seize and go lumpy – leave it for 10 minutes and even though it won’t look melted it will be fine,” says cookbook author Donal Skehan.

Donal Skehan’s perfect fudgy dark and white ripple brownies with raspberries

Ingredients:(Makes 16 squares)

100g (3½oz) dark chocolate, broken into pieces100g (3½oz) white chocolate, broken into pieces150g (5oz) unsalted butter, softened200g (7oz) caster (superfine) sugar75g (3oz) soft light brown sugar3 large free-range eggs1tsp vanilla bean paste150g (5oz) plain (all-purpose) flour150g (5oz) raspberries

Method:

1. Preheat the oven to 180°C/160°C fan/350°F/Gas 4 and grease and line a 20cm (8in) square cake tin with baking parchment.

2. Melt the dark chocolate in a heatproof bowl set over a pan of just simmering water. Set aside to cool a little bit. Do the same with the white chocolate in a separate bowl.

3. With a hand-held electric whisk, beat the butter and both sugars together until light and fluffy. Beat the eggs together in a small jug then gradually pour them into the butter and sugar mixture, whisking the whole time until you have a fluffy smooth mix. Beat in the vanilla bean paste and then the flour. Divide the mixture in half.

4. Gently fold the melted dark chocolate into one half of the mixture and the white chocolate into the other half.

5. Roughly dollop the mixture like a checkerboard into the prepared tin and push the raspberries into the mixture. Us the end of a teaspoon to swirl the two colours together.

6. Bake the brownies for 35–40 minutes so that a skewer comes out almost clean but still a little bit sticky. Leave to cool completely in the tin before cutting into squares. These taste even better the next day so try not to eat them all straight away!

Recipe from Everyday Cook by Donal Skehan, published by Hodder & Stoughton, priced £25. Available now.