1. Preheat the oven to 180ºC/ 350ºF/Gas 4. Line a 20 cm (8 in) square cake tin with baking parchment.

2. Put the butter, sugar, and dark chocolate in a large heatproof bowl. Set it over a saucepan of warm water. Let the butter and chocolate melt, stirring occasionally. Remove the bowl from the saucepan and leave to cool.

3. Prepare the orange zest and juice. Then whisk these together with the eggs, vanilla, and salt until combined. Whisk the orange and egg mixture into the cooled melted chocolate.

4. Sift the flour, cocoa powder, and baking powder onto the chocolate mixture and fold it in. Now add the white chocolate chips and fold these in too.

5. Pour into the prepared tin. Bake for 30 minutes if you want fudgy brownies or for 35 minutes for cakey brownies.

6. When done, let the brownies cool completely in the tin before tipping out. Cut into squares and serve.