First make the sponge. Whisk the flour, yeast and sugar together in a medium bowl. Stir in the water, cover the bowl with plastic wrap and leave in a warm place to rise until bubbly. About half an hour. Meanwhile melt the butter in the microwave or in a small saucepan and let it cool.

Preheat your oven to 350 degrees Fahrenheit and place a rack in the middle of your oven. Lightly butter a muffin tin.

In a large bowl sift the sugar, flour and cocoa powder together. Make a well in the center and add the butter, eggs and yeast mixture. Whisk the wet ingredients together, gradually drawing in the dry ingredients until they’re all incorporated. Lastly stir in the chocolate.

Spoon or pipe the batter into the tin, filling the forms to the rim. Bake them for 15 to 18 minutes until almost firm to the touch. While they’re still warm sift on a dusting of cocoa powder.