Preheat the oven to 180oC/Gas Mark 4. Grease a 28x18x2.5cm (11x7x1in) baking tin or brownie tin and line with greaseproof paper.
Put the chocolate Melts into a heatproof bowl set over a pan of hot, but not boiling, water, making sure the base of the bowl does not touch the water. Leave to melt, stirring occasionally, then remove the bowl from the pan. Alternatively, microwave in 30-second increments until melted.
Whisk the butter and sugar together in a bowl until light and fluffy. Gradually add the eggs, beating well after each addition.
Add the vanilla extract and the cacao chocolate and stir in gently using a spatula. Sieve the flour and cocoa powder into the bowl, then fold in the nuts until the mixture is combined.
Spoon the mixture into the prepared tin and spread evenly, then place on the middle shelf of the oven.
Bake for 25-35 minutes until the mixture feels firm when pressed, but not too hard! Remove from the oven and cool in the tin on a wire rack. When cold, cut the brownie into 24 squares and dust with icing sugar or cocoa powder. They can be served warm with a touch of cream – enjoy!