Pre-heat the oven to 160 degrees (fan forced oven) and grease and line a slice tin with baking paper.
Melt the butter and stir in the cocoa. Allow mixture to cool slightly. In a separate container whisk the eggs and then mix them into the cocoa and butter mixture.
Mix in the sugar and the vanilla.
Sift flour and baking powder together into the mixture and stir until thoroughly mixed through.
Stir in the chocolate chips.
Bake for 35-40 minutes (due to the differences in ovens it is best to check after 30 mins) or until just firm when pushed in the centre. Leave in the tin for twenty minutes to cool, and then lift out onto a cooling rack. When cold cut into slices.
Notes & Tips
I use Nestle Bites and Nestle cooking Cocoa in this recipe