01 - Combine flour, cocoa powder, yeast, sugar, and salt in a large mixing bowl.
02 - Pour in warm milk, melted butter, and egg. Stir until a sticky dough forms.
03 - Knead by hand or stand mixer for 8-10 minutes until smooth and elastic.
04 - Place dough in a greased bowl, cover, and let rise in a warm area until doubled, approximately 1 hour.
05 - Punch down dough and roll into a 16x12-inch rectangle on a floured surface.
06 - Spread softened butter evenly across the rolled dough.
07 - Mix brown sugar, cocoa powder, and cinnamon. Sprinkle mixture over buttered dough.
08 - Scatter dark chocolate chips over the sugar-cinnamon layer.
09 - Roll dough tightly from the long edge into a log. Cut into 12 equal pieces.
10 - Arrange rolls in a greased 9x13-inch baking dish. Cover and let rise until puffy, 30-45 minutes.
11 - Heat oven to 350°F.
12 - Bake for 22-25 minutes until rolls are set and lightly browned.
13 - Whisk powdered sugar, cocoa powder, milk, and vanilla until smooth.
14 - Drizzle chocolate glaze generously over warm rolls before serving.