In a large mixing bowl, combine sourdough starter, dark brown sugar, and warm milk. Stir until smooth, then add melted butter, egg, and salt.

Gradually incorporate bread flour until the dough starts pulling away from the bowl's sides.

Transfer the dough to a lightly floured surface and knead for about 5 minutes until smooth and slightly tacky.

Place the kneaded dough in a greased bowl, cover with a kitchen towel, and let rise for 3-7 hours until doubled in size.

Gently punch down the dough, roll it out to a rectangle, and spread softened butter. Sprinkle cinnamon and sugar mix, then roll tightly into a log.

Cut the log into 9 even pieces.

Arrange rolls in a greased baking dish, cover, and let rise for another 2-4 hours until puffy.

Preheat oven to 350°F (175°C). Pour heavy cream over the rolls before baking.

Bake for 30-35 minutes until tops are golden brown.

While the rolls bake, prepare frosting by beating cream cheese and butter until combined, adding powdered sugar until smooth.

Once baked and slightly cooled, drizzle cream cheese frosting over warm rolls.