Cut butter into cubes. Coarsely chop 200 g chocolate and nougat and melt with the butter in a saucepan over low heat while stirring. Beat the eggs with the whisk of the hand mixer for about 3 minutes until frothy.
Add the butter-chocolate mixture, flour and baking powder one after the other. Mix to a smooth dough.
Line recesses of a muffin tray (12 recesses) with paper cups. Spread half of the dough into the troughs. Sprinkle brittle on top and cover each with 1 piece of chocolate. Fill up with the rest of the dough.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 20 minutes. Remove the baked muffins from the tin and let them cool down on a cake rack for about 20 minutes.
Arrange on a plate.