Once the dough has risen, punch down and turn out onto a floured surface. Roll into a large rectangle. Smear the softened 1/4 cup butter all over the rectangle. Combine the sugar and cocoa and then sprinkle over the butter. Sprinkle on the chopped chocolate. Roll up into a long cylinder. Cut in about 8-10 rolls (if you cut slightly more or less, that's OK too). Place in a buttered pie pan or square pan.
In a large bowl, whisk together the powdered sugar, cocoa, vanilla, and 3 tablespoons milk. If the mixture seems too thick, add another tablespoon of milk until you get an Elmer's Glue-like consistency (like chocolate donut glaze). Drizzle over the rolls and topped with crushed candy canes if using.