Grease the mini bundt pan and dust with flour. Preheat the oven to 210 ° C top / bottom heat.
Mix the melted butter with the powdered sugar until smooth. Add the egg and beat very frothy. Melt the chocolate over a water bath and stir in. Stir milk into the mixture. Sieve the flour and cocoa together and fold into the mixture.
Pour the dough into the Gugelhupf pan using a piping bag and bake in the lower third of the preheated oven for about 11 minutes. Then take it out of the oven, let it cool down and remove it.