Gently fold in the melted butter. Sift the flour, cocoa and baking powder over the surface and fold in using a large metal spoon, trying not to knock out too much air. Divide the mixture between the cases, then bake for 15-20 mins until well risen and the sponge springs back when gently pressed. Leave to cool in the tins for 5 mins, then lift out onto a rack.
Healthy chocolate brownies
Heat the oven to 190C/170C fan/gas 5 and line a shallow 23cm square baking tin with baking parchment. Tip the beans, cocoa, coffee granules, xylitol, vanilla, eggs and yogurt into a large bowl. Blitz using a hand blender until smooth. Or, do this in a food processor. Add the baking powder, then blitz again.