In a stand mixer, combine the active sourdough starter, dark brown sugar, and warm whole milk until smooth.

Add in the melted unsalted butter, large egg, and salt, mixing until thoroughly incorporated.

Gradually add the bread flour until the dough pulls away from the sides of the bowl and feels tacky.

Knead the dough on a floured surface for about 5 minutes until smooth and elastic.

Transfer the kneaded dough into a greased bowl, cover, and let rise for 3-7 hours until doubled in size.

Roll the dough into a rectangle, spread softened butter, and sprinkle with cinnamon-sugar mixture. Roll tightly and cut into 9 pieces.

Place into a greased baking dish and let rise for an additional 2-4 hours until puffy.

Preheat oven to 350°F (175°C). Pour heavy cream over the rolls and bake for 30-35 minutes until golden brown.

Cool slightly and prepare the frosting by mixing powdered sugar, cream cheese, and heavy cream until smooth. Spread over rolls.