01 - Whisk together flour, cocoa powder, instant yeast, granulated sugar, and salt in a large mixing bowl until thoroughly combined.
02 - Pour warm milk, melted butter, and egg into the dry mixture. Stir with a wooden spoon 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, until smooth, elastic, and no longer sticky.
04 - Place dough in a greased bowl, turning to coat all sides. Cover with plastic wrap or a clean 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. Roll out on a floured surface into a 16x12-inch rectangle, ensuring even thickness throughout.
06 - Spread softened butter evenly over the entire surface of the rolled dough using a pastry brush or offset spatula.
07 - Combine brown sugar, cocoa powder, and cinnamon in a small bowl. Mix well to break up any lumps.
08 - Sprinkle the sugar-cocoa mixture evenly over the buttered dough, leaving a 1/2-inch border along the edges. Scatter chocolate chips over the top.
09 - Starting from one long edge, roll the dough tightly into a log, pressing gently to seal the seam. Position the roll seam-side down.
10 - Using a sharp knife or unflavored dental floss, cut the log into 12 equal rolls, approximately 1 1/2 inches wide.
11 - Arrange rolls in a greased 9x13-inch baking dish, leaving space between each. Cover and let rise in a warm place until puffy and nearly doubled, 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, springs back lightly when touched, and tops are just lightly browned. Avoid overbaking to maintain moisture.
14 - While rolls cool slightly, whisk powdered sugar, cocoa powder, 2 tablespoons milk, and vanilla in a medium bowl until smooth. Add additional milk 1 teaspoon at a time to reach desired consistency.
15 - Drizzle warm chocolate glaze generously over the slightly cooled rolls. Serve warm for best texture and flavor.