In a mixing bowl, combine light brown sugar, black cocoa powder, and ground cinnamon until evenly mixed. Set aside.

In the bowl of a stand mixer, whisk together all-purpose flour, unsweetened cocoa powder, instant dry yeast, instant espresso powder, and fine salt until well incorporated. Heat whole milk, granulated sugar, and unsalted butter until warm, then pour into dry ingredients.

Add large egg into the dough mixture and mix on medium speed until smooth and elastic, about 5 minutes. Let dough rest covered for around 15 minutes.

Turn dough out onto a floured surface and roll into a rectangle (¼ inch thick). Spread softened unsalted butter over the dough and sprinkle prepared filling evenly. Roll tightly to form a log shape.

Cut rolled dough into pieces, roughly 1½ inches thick. Place in a greased baking pan, cover, and let rise for approximately 30 minutes until doubled in size.

Preheat oven to 350°F (175°C). Bake rolls for 26-32 minutes until golden brown.

Prepare glaze by melting unsalted butter and chocolate chips together in a saucepan over low heat. Stir in whole milk, whisk in powdered sugar and vanilla extract until smooth.

Drizzle warm glaze over baked chocolate cinnamon rolls. Let cool slightly before serving.