In a medium bowl, combine the light brown sugar, black cocoa powder, and ground cinnamon until well blended. Set this rich chocolatey filling aside.

In a large mixing bowl, whisk together all-purpose flour, unsweetened cocoa powder, instant dry yeast, fine salt, and instant espresso powder. In a saucepan, warm the whole milk, granulated sugar, and unsalted butter until slightly warm. Combine this with the dry ingredients, adding a large egg, and mix until a soft, elastic dough forms. Allow the dough to rest for 15 minutes.

On a floured surface, roll out the rested dough into a 12x18 inch rectangle, about 1/4 inch thick. Spread softened butter evenly over the surface, then sprinkle the prepared filling over it, gently patting it down.

Starting at one long edge, roll the dough tightly into a log, then slice it into 9 equal pieces and place in a greased 9x13 inch pan.

Cover the pan with a clean kitchen towel and place it in a turned-off oven to rise for 30 minutes.

Preheat your oven to 350°F and bake the rolls for 26-32 minutes until the tops are lightly golden.

While the rolls are baking, melt unsalted butter, chocolate chips, and milk in a saucepan, stirring until smooth. Remove from heat and whisk in powdered sugar and vanilla extract until the glaze is glossy.

Once the rolls are out of the oven, drizzle the warm glaze over each roll and allow them to cool slightly before serving.