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, cohesive dough forms.
03 - Knead by hand on a floured surface or with a stand mixer for 8 to 10 minutes until smooth and elastic.
04 - Place dough in 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 into a 16x12-inch rectangle on a lightly floured surface.
06 - Spread softened butter evenly across the entire surface of the rolled dough.
07 - Stir together brown sugar, cocoa powder, and cinnamon in a small bowl.
08 - Sprinkle the sugar-cocoa mixture over the buttered dough, then scatter chocolate chips on top.
09 - Starting from a long edge, roll the dough tightly into a log. Cut into 12 equal portions.
10 - Place rolls in a greased 9x13-inch baking dish. Cover and let rise until puffy, 30 to 45 minutes.
11 - Heat oven to 350°F.
12 - Bake for 22 to 25 minutes until rolls are set and lightly golden brown on top.
13 - While rolls cool slightly, whisk powdered sugar, cocoa powder, milk, and vanilla until smooth.
14 - Drizzle chocolate glaze generously over warm rolls before serving.