In a stand mixer, combine flour, cocoa powder, brown sugar, and salt. Gradually add warm milk, egg, and softened butter. Mix until soft and slightly sticky.

Cover the dough and let it rise in a warm area for 1½ to 2 hours until doubled in size.

Prepare the filling by mixing brown sugar, cocoa powder, cinnamon, and vanilla extract until well combined.

Roll the dough out into a rectangle, spread with softened butter, and sprinkle the filling evenly. Roll tightly and slice into 9-11 pieces.

Place the rolls in a greased baking dish and let them rise for 30 to 60 minutes.

Preheat oven to 350°F (180°C) and bake for approximately 20 minutes until golden brown.

Prepare the glaze by whisking together powdered sugar, cocoa powder, and heavy cream until smooth.

Once baked, let rolls cool slightly and drizzle with glaze.