01 - Combine flour, cocoa powder, instant yeast, granulated sugar, and salt in a large mixing bowl. Whisk thoroughly to ensure even distribution of leavening agent and cocoa.
02 - Pour warm milk, melted butter, and beaten egg into dry ingredients. Mix with a wooden spoon or dough hook until a sticky, shaggy dough forms.
03 - Turn dough onto a lightly floured surface and knead by hand for 8-10 minutes, or use a stand mixer with dough hook. Work until smooth, elastic, and slightly tacky but not sticking to hands.
04 - Place dough in a lightly greased bowl, turning once to coat all surfaces. Cover with plastic wrap or a damp towel and let rise in a warm, draft-free area until doubled in bulk, approximately 1 hour.
05 - Punch down risen dough to release air. Turn onto a floured surface and roll into a 16x12-inch rectangle, maintaining even thickness throughout.
06 - Spread softened butter evenly over the entire surface of the rolled dough, leaving a 1/2-inch border along one long edge.
07 - Combine brown sugar, cocoa powder, and cinnamon in a small bowl. Mix thoroughly to break up any lumps.
08 - Sprinkle the brown sugar mixture evenly over the buttered dough. Scatter chocolate chips across the surface, pressing gently to adhere.
09 - Starting from the long edge opposite the 1/2-inch border, roll dough tightly into a cylinder. Pinch the seam firmly to seal.
10 - Use unflavored dental floss or a sharp knife to cut the log into 12 equal pieces, approximately 1 1/4 inches thick.
11 - Place rolls cut-side up in a greased 9x13-inch baking dish, spacing evenly. Cover loosely and let rise in a warm spot until puffy and noticeably expanded, 30-45 minutes.
12 - Preheat oven to 350°F during the final 15 minutes of the second rise.
13 - Bake for 22-25 minutes until rolls are set, spring back lightly when touched, and show golden brown edges. Avoid overbaking to maintain moisture.
14 - While rolls cool in the pan for 5-7 minutes, whisk powdered sugar, cocoa powder, 2 tablespoons milk, and vanilla extract in a small bowl. Add additional milk 1 teaspoon at a time until reaching drizzling consistency.
15 - Drizzle warm chocolate glaze generously over slightly cooled rolls. Serve immediately while still warm for optimal texture and flavor.