01 - Whisk together flour, cocoa powder, instant yeast, sugar, and salt in a large mixing bowl until thoroughly combined.
02 - Pour warm milk, melted butter, and beaten egg into the dry ingredients. Stir with a wooden spoon until a sticky, shaggy dough forms.
03 - Knead on a lightly floured surface for 8-10 minutes until dough becomes smooth, elastic, and springs back when pressed. Alternatively, use a stand mixer with dough hook for 5-6 minutes on medium speed.
04 - Place dough in a greased bowl, turning once to coat all sides. Cover with plastic wrap or a warm damp towel. 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, approximately 1/4-inch thick.
06 - Spread softened butter evenly over the dough surface using an offset spatula, leaving a 1/2-inch border around edges.
07 - Combine brown sugar, cocoa powder, and cinnamon in a small bowl. Sprinkle mixture uniformly over buttered dough. Scatter dark chocolate chips across the sugar layer.
08 - Starting from a long edge, roll dough tightly into a log. Pinch seam to seal. Cut into 12 equal portions using unflavored dental floss or a sharp knife.
09 - Arrange rolls cut-side up in a greased 9x13-inch baking dish, leaving space between each. Cover loosely and let rise until puffy and nearly doubled, 30-45 minutes.
10 - Preheat oven to 350°F with rack positioned in center.
11 - Bake for 22-25 minutes until rolls are set, spring back lightly when touched, and edges are golden brown. Internal temperature should reach 190°F when fully baked.
12 - While rolls cool for 10 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 pourable consistency.
13 - Drizzle warm glaze generously over slightly cooled rolls. Serve immediately while still warm for best texture and flavor.