These brownies are easy to make but look seriously impressive when served.
Prep time: 30 minutes
Cook time: 50 minutes
200g unsalted butter, chopped, plus extra for greasing
100g dark chocolate (70% cocoa solids), chopped
100g white chocolate, chopped
3 medium eggs
300g caster sugar
100g plain flour, sifted
1. Preheat the oven to gas mark 4/180°C/fan over 160°C. Thickly butter an 18cm square cake tin and line the base with baking parchment. Set aside.
2. Divide the butter between 2 heatproof bowls. Add the white chocolate to one bowl and place over a saucepan of simmering water, making sure the water doesn't come near the bottom of the bowl. Heat, stirring occasionally, for 3-5 minutes or until the chocolate has melted. Remove from the heat and set aside.
3. Add the dark chocolate to the remaining bowl of butter and heat that over the water, stirring occasionally, until melted. Remove from the heat and set aside.
4. In a separate mixing bowl, whisk the eggs and caster sugar together for 3-5 minutes with an electric whisk or until thick and pale. Spoon half the mixture into the white chocolate bowl and, using a flexible rubber spatula, fold the chocolate and egg mixtures together, trying not to knock out too much air.
5. Fold the remaining egg mixture into the dark chocolate. Sift 50g plain flour into each chocolate mix and fold in to combine.
6. Drop spoonfuls of the two mixtures into the cake pan to make a patchwork pattern of cake mixture. Drag a skewer through the mix a couple of times to marble it. Bake for 30 minutes or until a crust has formed (a skewer inserted should come out slightly messy).
7. Cool in the tin, then slice into 12 brownies and carefully lift out - they should be squidgy in the middle. The brownies will keep for about a week in an airtight container, but it's unlikely they'll last more than 24 hours.