In a large bowl, whisk together the active sourdough starter and milk until the starter is fully dissolved. Next, whisk in the sugar and room temperature egg until well incorporated.

Sift the flour and salt into the bowl, stirring until a shaggy dough begins to form. Then, add the room temperature butter, mixing either by hand or with a stand mixer until fully incorporated. It is important to use room temperature butter or this step will be difficult. You can test the butter’s softness by pressing your finger into it. If you can easily push all the way through without resistance, then the butter is ready.

After mixing, cover the dough with a damp cloth and allow it to rest for 20 minutes.

Uncover the dough and knead it on medium speed with a dough hook attachment for approximately 12 minutes. The dough is ready when it becomes smooth and pulls away from the sides of the bowl. If working without a stand mixer strengthen the dough by hand. To do this perform three sets of stretch and folds. Strengthening the dough will develop more gluten structure and give your cinnamon rolls more body and rise. However, it's important to note that this recipe has been formulated and tested to not require any kneading, and the rolls will be delicious without this step.

Cover the bowl with a damp cloth to bulk ferment the dough at 72°F(21°C), or room temperature, for 9-10 hours, or overnight. The dough will need to rise until it is double its original size. It’s important to note that rise times can vary based on the temperature in your home, so adjust the time accordingly.

Before turning out the dough, lightly dust your work surface with flour. Gently pat the dough into a rectangular shape and use a floured rolling pin to roll it out into a 12″x18″ rectangle.

In a bowl, whisk together the brown sugar and cinnamon to make the filling, then set it aside.

Spread the room temperature butter over the sheet of sweet dough, leaving a one-inch margin along the length of the dough. This margin will help to seal the rolls when you roll up the dough.

Next, spread the cinnamon sugar mixture on top of the layer of butter and roll dough up tightly. Start with the end opposite of the margin and roll inwards applying a gentle pressure.

Lightly wet the margin with water before sealing. Allow the roll to rest, seam side down, for a minute to ensure a tight seal. Using a non-serrated knife, cut the log into twelve equally-sized cinnamon rolls. Wetting your knife every few cuts will prevent the dough from pulling and give clean slices.

Arrange the cut rolls in a 9″x13″ pan, ensuring they are evenly spaced apart. If preferred, using a slightly smaller pan will yield doughier cinnamon rolls. Place a cloth or kitchen towel over the pan, ensuring the rolls are well covered.

Let them rise at a temperature of around 72°F (21°C), or room temperature, for 2-4 hours. During this second rise, the rolls will increase in size and become visibly poofy. It’s important to note that rise times can vary based on the temperature in your home, so adjust the time accordingly. See notes for a way to speed up second rise times.

Position your rolls on the center rack of a 350°F (177°C) preheated oven and bake for 25-30 minutes.

While the rolls are baking, prepare the frosting. Using an electric mixer or stand mixer, beat together the cream cheese, butter, powdered sugar, and milk until you achieve a creamy, lump-free frosting. Add more or less milk as needed to achieve your desired consistency.

Once out of the oven allow the sourdough cinnamon rolls to cool for 15 minutes before frosting. Serve and enjoy!