1. Preheat the oven to 180°C (160°C fan) or 350°F and line a 30x20cm baking tray with parchment paper.

2. Cream the butter and brown sugar together until light and fluffy.

3. Beat in the eggs one at a time, adding a teaspoon of flour if the mixture curdles, then stir in the vanilla extract.

4. Sift the flour, cocoa powder, and baking powder into the bowl and fold gently until just combined.

5. Stir in the milk and chopped nuts until evenly distributed.

6. Pour the batter into the prepared tray and spread to the corners, then gently level the surface.

7. Bake for 25–30 minutes until the top is springy and a skewer comes out clean.

8. Allow to cool in the tin for 10 minutes, then lift out using the parchment and cool completely on a wire rack.

9. Decorate with melted chocolate drizzle, chopped nuts, or a dusting of cocoa powder before cutting into squares.