01 - Combine flour, cocoa powder, yeast, sugar, and salt in a large bowl.
02 - Add warm milk, melted butter, and egg to the dry mixture. Stir until a sticky dough forms.
03 - Knead by hand or with a stand mixer for 8-10 minutes until smooth and elastic.
04 - Place dough in a greased bowl, cover, and let rise in a warm place until doubled in volume, approximately 1 hour.
05 - Punch down dough and roll out on a floured surface into a 16x12-inch rectangle.
06 - Spread softened butter evenly over the rolled dough surface.
07 - Mix brown sugar, cocoa powder, and cinnamon. Sprinkle mixture evenly over the buttered dough.
08 - Scatter dark chocolate chips over the sugar-cocoa mixture.
09 - Starting from the long edge, roll up the dough tightly into a log. Slice into 12 equal rolls.
10 - Arrange rolls in a greased 9x13-inch baking dish. Cover and let rise until puffy, approximately 30-45 minutes.
11 - Preheat oven to 350°F.
12 - Bake for 22-25 minutes until rolls are set and lightly browned.
13 - While rolls cool slightly, whisk together powdered sugar, cocoa powder, milk, and vanilla extract until smooth.
14 - Drizzle glaze generously over warm rolls before serving.