Measure the flour and cocoa powder into a bowl. Add salt. Set aside.
In a large mixing bowl, add the yeast. Next, add the milk, eggs, and sugar.
Mix on medium-low speed for 2 minutes.
Sift the flour, cocoa powder, and salt into the mixing bowl.
Mix all the ingredients on medium-low speed for 5 minutes, until they come together.
Cut butter into small pieces and add it slowly into the dough (while the mixer continues to knead) over 2 minutes. The dough will appear very sticky at this stage.
Once the butter is all incorporated, stop the mixer. Scrape the sides of the bowl.
Knead again at medium-low speed for 15 minutes. At this stage, the dough will be very soft and tacky.
Turn the dough out onto your workspace and bring it together with a spatula or a scraper.
Place the chocolate brioche dough into a greased bowl. Cover with cling wrap and refrigerate for at least 8 hours or overnight.
Prepare a loaf tin. Grease it well and set aside.
Remove the dough from the fridge. Press out the air bubbles.
Divide it into 4 sections. Knead each section until smooth and form them into balls.
Arrange the balls into the loaf tin in a line. Flatten them on the sides so that they fit into the bread tin.
Let the brioche loaf proof again until slightly more than double in size.
Bake the chocolate brioche bread at 165°Celcius (in a preheated oven) on the lowest rack in the oven.
Once baked, remove the loaf from the oven and brush the top with melted butter.
Let the bread loaf rest in the tin for about 1 minute. Turn it out onto a wire rack to cool completely.
Slice the bread after it has completely cooled down for neater slices.