For the mug cake, first separate the egg whites from the yolks and beat the egg whites until stiff. Then beat the egg yolks, butter and powdered sugar with the vanilla sugar until fluffy.
Add the flour, almond milk and baking powder to the bowl. Meanwhile, grease the cake pan with butter and breadcrumbs and pour some of the finished cake mixture into it.
Mix the rest of the mixture with cocoa powder and add it to the cake pan. Bake the cake at 180 °C, top and bottom heat for about 45-50 minutes.