In a stand mixer fitted with a whisk attachment, thoroughly combine the warm milk, yeast, egg, sugar, salt, and 3 tablespoons of melted butter in the bowl.
1¾ cups whole milk, 2¼ teaspoons instant yeast, 1 large egg, 3 tablespoons granulated sugar, ½ teaspoon salt, 6 tablespoons salted butter
Switch to a dough hook and add in the bread flour and mix on "stir" speed for 3 minutes. You will need to scrape down the sides of the bowl once or twice, while mixing.
4½ cups bread flour
After 3 minutes, touch the dough with a clean dry finger. If the dough doesn’t stick to your finger, it is ready. If it does, add additional flour 1 tablespoon at a time, mixing as you go until the dough doesn’t stick to your finger when you test it. (SEE NOTES ON CHECKING DOUGH)
When the dough is ready, it should feel tacky and pliable. Add a small drizzle of vegetable or canola oil to a large clean bowl and turn your dough out into it. Rotate the dough so that it’s oiled on all sides then cover it with cling wrap and let rise somewhere warm for 1 hour. It should double in size within that time.
1 tablespoon vegetable or canola oil
Meanwhile, prepare the filling by mixing together the softened butter, brown sugar, cinnamon, and cocoa powder in a bowl until thoroughly combined. Set aside.
¼ cup salted butter, 3 tablespoons dark brown sugar, 2 tablespoons ground cinnamon, 2 tablespoons dutch-processed cocoa powder
Once the dough has doubled in size, punch it down in the center, then transfer it to a lightly floured surface. Use your hands to shape the dough into a rectangular shape, then roll it out into a 16x8-inch rectangle measuring; it doesn’t have to be exact.
Spread the chocolate and cinnamon filling over the surface of the dough, leaving a border of about ¼-inch around the edge.
Sprinkle the chopped chocolate over the top of the cinnamon mixture and use your hands to gently press the chocolate into the dough so that it doesn’t escape when you roll it up.
¾ cup semi-sweet chocolate
Wash your hands before you begin rolling so none of the chocolate transfers to the outside of the rolls. With the longest edge facing you, tightly roll up the dough into a log shape. When you’re done rolling, pinch the seem together with your fingertips, then cut the dough log in the middle. I like using unflavored dental floss to cut the dough. Simply slide it under the log, bring the floss up around the side, cross it, and then pull it to cut through the dough - this prevents squeezing the dough and helps it hold its circular shape.
Cut each half of the log into 6 equal pieces using the dental floss for best results. You can eyeball it or measure it with a ruler for accuracy. Our rolls were 1¾-inch each.
Grease a large 9x13-inch baking dish with 1 tablespoon of melted butter, then arrange the Chocolate Cinnamon Rolls so that there is a little room in between each one. Cover with cling wrap and leave somewhere warm for 30 minutes. The rolls will puff up in size during that time.
1 tablespoon salted butter
Meanwhile, preheat the oven to 350ºF.
Once risen, brush the rolls with 2 tablespoons of melted butter.
2 tablespoons salted butter
Bake the dish on the center of the oven and bake for 22 minutes or until golden brown. The center of the rolls should read 190°F on an instant-read thermometer when done. Transfer the dish to a wire rack to cool.
While the rolls cool, prepare the chocolate glaze by adding cocoa powder, powdered sugar, and milk to a bowl. Whisk until thoroughly combined. The glaze will be a thin, pourable consistency.
4 tablespoons dutch-processed cocoa powder, 1 cup powdered sugar, 4 tablespoons whole milk
Pour about ¾ of the glaze directly on top of the Chocolate Cinnamon Rolls while they are still in the baking dish.
Remove from the dish and drizzle extra chocolate glaze over them and serve while still warm and gooey from the oven!