Line a 20cm square pan with baking paper, with some overhang over the side of the tin.
Combine all of the dry ingredients in a large bowl.
Break up chocolate into a microwave safe container and melt in the microwave in 30 second bursts, stirring after each interval.
Pour melted chocolate over the dry mixture and combine, mixing quickly before the chocolate starts to set.
Pour mixture into pan and smooth down with a spatula.
Allow to set in the fridge for at least 45 minutes.
Remove from pan and cut into pieces to serve.