Brush an oven dish with butter to prevent it from sticking.
Cut the croissants into pieces and place them in the baking dish.
Sprinkle half of the chocolate chips over the croissants. We'll need the rest tomorrow.
Beat the eggs until they are creamy. Add the chocolate milk, the heavy cream, brown sugar, vanilla sugar and cinnamon in succession. Beat until everything is well mixed.
Carefully pour the mixture over the croissants. Give them time to soak up the liquid.
Cover the bowl and refrigerate for at least four hours. Better yet, let them soak all night.
Baking
Preheat the oven to 175°C.
Sprinkle the rest of the chocolate chips over the dish.
Bake the dish in the oven for 50 minutes.
Remove the dish from the oven and let it cool down for 5 minutes. Then cut and enjoy!