In a small bowl, combine warm milk with active dry yeast and let it sit for 5–10 minutes until frothy.

In a stand mixer, whisk together flour, cocoa powder, brown sugar, and salt. Add egg, melted butter, and yeast mixture, and mix until ingredients combine.

Transfer the dough to a greased bowl, cover, and let rise in a warm area for 1½ to 2 hours until doubled.

In a medium bowl, mix brown sugar, cocoa powder, cinnamon, and vanilla extract until smooth to prepare the filling.

Roll the risen dough into a rectangle, butter it, sprinkle the filling, and roll tightly, slicing into 9–11 pieces.

Place rolls in a greased dish, cover, and let rise for 30–60 minutes until puffy.

Preheat oven to 350°F and bake rolls for about 20 minutes until golden brown.

Whisk powdered sugar, cocoa, and heavy cream for the glaze, then pour over warm rolls after baking.