For the power muffins, melt the butter and let cool (otherwise the chocolate will melt).
Mix the flour, sugar, baking powder and salt briefly with a wooden spoon.
In a separate saucepan, whisk together milk, eggs and vanilla sugar. Stir together butter, flour mixture, egg-milk mixture, and chopped dark chocolate (not with a mixer!!!) – just until everything is blended!
Bake the power muffins for 20 to 25 minutes at 175 degrees.