Boil the milk and coffee in a pot. Reduce the heat to minimum, add 70g of milk chocolate. Stir until the chocolate melts. Make sure that the mixture now is warm, but does not boil.
Add cocoa powder and butter. Continue stirring until the butter melts, the contents of the pot become homogeneous and all cocoa lumps are gone.
Remove the pot from the heat and set aside to cool to room temperature. Then add oil, 2 eggs, vanilla extract and mix well with a kitchen whisk.