Warm milk to 110°F. Stir in yeast + 1 tablespoon of the sugar. Rest 5 minutes until foamy.
Add remaining sugar, melted butter, cocoa powder, and egg. Mix until combined.
Mix in flour and salt until a dough forms. Knead 8 minutes until smooth and elastic.
Place in greased bowl, cover, and rise 60–90 minutes until doubled.
Beat softened butter, brown sugar, cocoa powder, and vanilla until spreadable.
Roll into a 12x18-inch rectangle on a lightly floured surface.
Spread filling evenly, leaving a 1-inch border. Sprinkle mini chocolate chips over the top.
Roll into a tight log from the long side. Cut into 12 rolls using floss or a sharp knife.
Arrange rolls in greased 9x13 dish. Cover and rise 45–60 minutes until puffy.
Bake at 350°F for 20–25 minutes until set and lightly golden.
Beat cream cheese, marshmallow fluff, and butter until smooth. Add powdered sugar, then vanilla + milk to a thick, spreadable texture.
Spread frosting over warm rolls. Top with mini marshmallows, chocolate shavings, and drizzle with chocolate syrup.