(slightly adapted from: Leila Lindholm - Piece of Cake)
Grated zest of one lemon
1 tsp vanilla extract/vanilla sugar
240g plain flour
2 tsp baking powder
1 pinch of salt
Grated zest of two oranges
200g dark chocolate, broken into pieces
Preheat oven to 180°C. Line a muffin tray with 12 moulds with paper cups.
Melt butter in a little saucepan, let cool slightly. Then, add lemon zest and milk. In a bowl, beat eggs, sugar and vanilla until foamy. Add the lukewarm butter-milk-mixture. Add orange zest. Then, sift in flour, baking powder and salt. Mix until well combined. Add about 3/4 of the chocolate and mix well.
Fill the dough into your prepared paper cups. Top with the remaining chocolate pieces. Bake for about 20 minutes.