Activate Yeast: In a small bowl, combine warm milk (about 110°F/43°C) with active dry yeast and let sit for 5-10 minutes until foamy.

Dough Preparation: In a large stand mixer bowl, combine all-purpose flour, cocoa powder, brown sugar, and salt. Pour in yeast mixture, egg, and softened butter. Mix on medium speed for approximately 3 minutes.

First Rise: Cover the bowl and place it in a warm area to rise for 1½ to 2 hours, until dough doubles in size.

Filling Mix: Mix brown sugar, cocoa powder, cinnamon, and vanilla extract in a bowl until smooth.

Roll Out Dough: Transfer risen dough to a floured surface and roll into a ¼ inch thick rectangle. Spread softened butter and then the filling on top.

Form Rolls: Roll dough tightly into a log and cut into 9-11 equal segments.

Second Rise: Place the cut rolls in a greased baking dish and let them rise for an additional 30-60 minutes.

Baking: Preheat oven to 350°F (180°C). Bake rolls for about 20 minutes, until golden brown.

Glaze Preparation: Whisk together powdered sugar, cocoa powder, and heavy cream until smooth and glossy.