Makes 12

  1. Pre-heat the oven to 190°C/375°F/Gas 5. Put the chocolate and butter in a heatproof bowl over a pan of simmering water, and stir until melted.  Alternatively, put the chocolate and butter into a suitable bowl, microwave for 1 minute, stir, then microwave in 10-second blasts until melted. Allow to cool slightly.
  2. Using an electric mixer, whisk the eggs and maple syrup. Stir in the chocolate and then sift and fold in the flour, cocoa, baking powder and a large pinch of salt.
  3. Line a 28 cm x 20 cm (14 in x 8 in) cake tin with baking parchment, with the parchment coming up the sides of the tin. Pour the mixture into the tin and bake for 20–25 minutes, until a crust has formed but there is some give underneath when pressed. Do not overbake. Remove from the oven and allow to cool thoroughly in the tin.  Don’t worry, it will sink and crack a little.
  4. Remove from the tin and cut into squares before serving. You can decorate the brownies with remaining walnuts