Chocolate Brioche :

1. Rehydrate the dry baker's yeast in the lukewarm milk, mix and set aside for 5 to 10 minutes.
2. In the bowl of a stand mixer fitted with the dough hook, first pour the dry ingredients, flour, sugar, unsweetened cocoa powder and salt and mix at medium speed.
3. Then, while leaving the mixer running, add the egg, the melted and cooled butter, the milk and yeast mixture and knead for about 3 minutes at medium speed until you obtain a homogeneous and soft dough ball.
4. Cover with a clean tea towel and leave to rise at room temperature for 1h30 - 2 hours until the dough doubles in size.  

Chocolate and cinnamon filling :

1. In a small bowl, combine the brown sugar, unsweetened cocoa powder, vanilla and cinnamon ground. 
2. Roll out the dough with a rolling pin on a floured work surface into a large rectangle about 0.5 mm thick. 
3. Spread the softened butter over the entire surface of the dough with an angled spatula or tablespoon.
   Pour in all the brown sugar, cinnamon and cocoa powder mixture and spread it with your hands or a spoon so that it sticks to the butter.
4. Roll the dough into a long log and cut into 9 - 11 pieces.
5. Place in a baking dish and space them about 5 cm apart.  
6. Let it rise a second time for about 30 minutes to 1 hour.

Baking :

1. Preheat the oven to 350°F / 180°C fan oven.
2. Bake the brioches for about 20 - 25 minutes, until they are puffed up.
3. Let them cool down a bit.

Chocolate glaze :

1. Put all the ingredients, powdered sugar, unsweetened cocoa powder and heavy cream in a small bowl.
2. Mix until you have a smooth and homogeneous icing.
3. Pour the glaze over the cinnamon rolls and serve lukewarm.