Melt the butter in a small pot. In a large bowl mix flour, baking powder, cocoa and sugar. Add liquid butter and about 100 ml warm water while stirring.
Line the 12 wells of a mini muffin tray with mini baking cups. Spread the dough in them. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for about 12 minutes. Take out of the oven and let cool down.