Preheat the oven to 190°C/Fan170°, 375°F, Gas Mark 5.
Combine the butter and chocolate in a heatproof bowl and melt together in a bowl set over a pan of simmering water for a few minutes. Don’t let the bowl touch the water. Alternatively, melt it in the microwave for about 1 minute. Stir well and leave to cool a little.
Lightly beat together the eggs and Tate & Lyle Light Muscovado Sugar in a bowl with a fork. Pour in the melted chocolate mixture and beat to combine. Sprinkle over the espresso powder, add the vanilla extract and mix. Sift in the flour, baking powder and salt, stir and then mix in the nuts.
Tip into the brownie tin and bake on the middle shelf of the oven for 20 minutes or until a crust has formed. Remove, leave to cool for 2 hours, then cover with cling film and chill for at least another 2 hours.
Turn out of the tin, discard the parchment and trim the edges, cut into squares, lightly dust with cocoa and serve.
If you like these, why not try some of our other brownies! We've got Pistachio, Gooey Caramel, and our notorious Brondies: a dark and white chocolate duo. One word, yum!