In a small bowl, combine warm milk and yeast; let sit for about 5-10 minutes until foamy.

In a stand mixer, combine flour, cocoa powder, brown sugar, and salt; mix, then add yeast mixture, egg, and softened butter.

Mix on medium speed for about 3 minutes until soft and slightly sticky.

Transfer dough to a greased bowl, cover, and let rise in a warm place until doubled in size (approximately 1½ to 2 hours).

For filling, combine brown sugar, cocoa powder, and ground cinnamon in a bowl and stir until mixed.

Once dough has risen, punch down, roll out on floured surface, spread butter, and sprinkle filling across the surface.

Roll dough tightly into a log, slice into 9-11 pieces, and arrange in a greased baking dish.

Let rolls rise for another 30-60 minutes until puffy and nearly touching.

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

For the glaze, combine powdered sugar, cocoa powder, and heavy cream; whisk until smooth, then drizzle over warm rolls.