01 - Combine flour, cocoa powder, yeast, sugar, and salt in a large mixing bowl.
02 - Pour warm milk, melted butter, and egg into dry ingredients. Mix thoroughly until a sticky, cohesive dough forms.
03 - Knead by hand on a floured surface or with stand mixer using dough hook for 8-10 minutes until smooth, elastic, and slightly tacky.
04 - Transfer dough to a lightly greased bowl, cover with plastic wrap or damp towel, and let rise in a warm, draft-free area until doubled in volume, approximately 1 hour.
05 - Punch down risen dough to release air. Roll out on a lightly floured surface into a 16x12-inch rectangle, approximately 1/4-inch thick.
06 - Spread softened butter evenly over the entire surface of rolled dough using offset spatula or pastry brush.
07 - Combine brown sugar, cocoa powder, and cinnamon in a small bowl. Mix until evenly incorporated.
08 - Sprinkle sugar-cocoa mixture uniformly over buttered dough. Scatter chocolate chips across the surface.
09 - Starting from one long edge, roll dough tightly into a log. Using sharp knife or unflavored dental floss, slice into 12 equal pieces, approximately 1 1/2 inches thick.
10 - Place rolls cut-side up in greased 9x13-inch baking dish, leaving space between each. Cover and let rise in warm area until puffy and visibly expanded, 30-45 minutes.
11 - Preheat oven to 350°F during final minutes of rising time.
12 - Bake for 22-25 minutes until rolls are set, spring back lightly when touched, and display minimal golden-brown coloration.
13 - While rolls cool slightly, whisk powdered sugar, cocoa powder, 2 tablespoons milk, and vanilla in medium bowl until smooth. Add additional milk if needed to reach drizzling consistency.
14 - Drizzle warm chocolate glaze generously over slightly cooled rolls. Serve immediately while still warm.