In a large mixing bowl, whisk together 1 cup of active sourdough starter and 1 cup of whole milk until smooth. Add in 1/2 cup of cane sugar and 1 whisked egg.

Sift 4 cups of bread flour and 1 teaspoon of sea salt into the wet mixture, stirring gently until a shaggy dough forms.

Add 1/4 cup of room temperature unsalted butter to the dough, mixing thoroughly until fully integrated.

Knead the dough on medium speed for about 12 minutes, or stretch and fold by hand, until it becomes smooth and elastic.

Transfer the kneaded dough to a lightly greased bowl, cover with a clean kitchen towel, and let it rise at room temperature for 8 to 9 hours.

Flour your work surface and roll out the dough into a large rectangle. Spread butter and sprinkle cocoa powder mixture with chocolate chips, then roll tightly and cut into 12 pieces.

Place the cut rolls into a greased baking dish, cover them, and let them rise for another 2 hours.

Preheat your oven to 350°F (177°C). Bake the rolls for 25 to 30 minutes until golden brown.

While the rolls are baking, prepare the frosting by boiling 1/4 cup of milk, 1 cup of powdered sugar, and 2 tablespoons of cocoa powder until thickened.