Prepare the Dough Ingredients: In the bowl of a stand mixer, combine warm milk, active starter, large eggs, melted butter, granulated sugar, and a little bit of the flour. Use the dough hook attachment to mix on low speed until a shaggy dough forms. Let it rest for 30 minutes.

Knead the Dough: After the dough rest, knead the dough at medium speed for 6-8 minutes until smooth and elastic. Perform a windowpane test to check if the dough is ready.

First Rise: Cover the dough and let it rise in a warm spot until it increases by 30% in volume. This bulk fermentation can take 8-12 hours, depending on room temperature. This is an important thing to consider if you're following a baker’s schedule.

Refrigerate Overnight Or Move to the Next Step: You can put the dough in the fridge to rest overnight, or if you're ready to keep going, move on to the next step in the recipe.

Prepare the Filling: While the dough is rising, prepare the cinnamon sugar mixture in a small bowl. Mix brown sugar, white sugar, and Ceylon cinnamon with softened butter.

Roll Out the Dough: If you’re making the rolls on the same day, let the dough rest for about 20-30 minutes after it rises. Then, roll it out on a floured surface. If you put the dough in the fridge overnight, take it out in the morning and let it warm up for 20 minutes before rolling it out. Spread the cinnamon filling evenly over the dough, but leave a small edge on one side without filling.

Shape the Rolls: Roll the dough tightly into a log and slice it into 1-inch pieces using a sharp knife. Place the unbaked rolls into a cast iron skillet or baking dish lined with parchment paper for best results. You can even shape them into little hearts using a Sweedish roll design.

Final Rise: Let the rolls have a final rise in a warm place until they double in size. This second time of rising ensures fluffy sourdough cinnamon rolls. For an extra indulgence, pour a bit of heavy cream over the unbaked rolls before baking.

Bake the Rolls: Preheat your oven to 350°F. Bake the rolls until they are golden brown on top, about 25-30 minutes.

Make the Frosting: While the rolls are baking, prepare the cream cheese frosting in a medium mixing bowl using an electric mixer at low speed. Combine cream cheese, powdered sugar, and vanilla extract until smooth.

Finish and Serve: Once the rolls are done baking, let them cool on a wire rack for a few minutes before spreading the frosting generously over the top.

Enjoy your fluffy sourdough cinnamon rolls warm from the oven!