Grease with butter and lightly flour a 12-hole madeleine mould. Melt the chocolate over a bain-marie (water bath) until it reaches 45°C (113°F) and leave to cool. Melt the butter in a saucepan and also leave to cool. Sift the flour, cocoa powder and baking powder into a bowl and then mix in the sugar. Add the dry ingredients to the beaten egg yolks in a large bowl and mi