01 - Combine flour, cocoa powder, yeast, sugar, and salt in a large mixing bowl.
02 - Pour in warm milk, melted butter, and egg. Mix thoroughly until a sticky, uniform dough forms.
03 - Knead by hand or using a stand mixer for 8-10 minutes until dough becomes smooth and elastic.
04 - Transfer dough to a greased bowl, cover, and let rise in a warm area until doubled in volume, approximately 1 hour.
05 - Punch down risen dough and roll out on a floured surface into a 16x12-inch rectangle.
06 - Evenly spread softened butter across the entire surface of the rolled dough.
07 - Combine brown sugar, cocoa powder, and cinnamon. Sprinkle mixture evenly over buttered dough.
08 - Distribute chocolate chips over the sugar-cinnamon mixture.
09 - Roll dough tightly from the long edge into a log. Cut into 12 equal slices.
10 - Place rolls in a greased 9x13-inch baking dish. Cover and let rise until puffy, 30-45 minutes.
11 - Preheat oven to 350°F.
12 - Bake for 22-25 minutes until rolls are set and lightly golden brown.
13 - While rolls cool slightly, whisk powdered sugar, cocoa powder, milk, and vanilla until smooth.
14 - Drizzle glaze generously over warm rolls immediately before serving.