Warm 1 cup of milk until just warm to touch; sprinkle active dry yeast and let sit for 5-10 mins until frothy.

In stand mixer, combine 4 cups flour, ½ cup cocoa powder, ½ cup brown sugar, and 1 teaspoon salt. Add yeast mixture, egg, and ½ cup butter, mix until dough forms.

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

In bowl, mix ½ cup brown sugar, ¼ cup cocoa powder, 1 tablespoon cinnamon, and 1 teaspoon vanilla until combined.

Roll risen dough into ¼ inch thick rectangle, spread ¼ cup butter, and sprinkle filling evenly. Roll tightly and slice into 9-11 pieces.

Place rolls in greased baking dish, cover, and let rise for another 30-60 minutes.

Preheat oven to 350°F (180°C). Bake rolls for about 20 minutes until golden brown and cooked through.

Whisk together 1 cup powdered sugar, ¼ cup cocoa powder, and ¼ cup cream until smooth. Drizzle over warm rolls.