Pro-tip: For the best results, be sure to use a kitchen scale for precise measurements. 

DOUGH

1. Add active starter, dark brown sugar and warm milk to the bowl of a stand mixer with the paddle attachment. Be sure that the milk isn’t boiling (no hotter than 120 F) – this could kill the starter and prevent the dough from rising.

   The dough can also be mixed and kneaded by hand. Increase the knead time to 8-10 minutes.

   Light brown sugar can be substituted for dark brown sugar.
   100 grams active sourdough starter, 175 grams warm milk, 30 grams dark brown sugar *see notes
2. Mix on low speed until the ingredients are mixed thoroughly.
3. To the bowl, add the melted unsalted butter, salt, and a large room temperature egg. Mix on low until fully combined.
   57 grams unsalted butter, melted, 5 grams salt, 1 large egg
4. Switch the paddle attachment with the dough hook attachment. Then, mix in the flour, adding 70g (1/2 c) at a time, and mix on medium until incorporated. Stop to scrape the sides of the bowl with a rubber spatula in between each addition of flour.

   You know the dough will have enough flour when the dough is pulling away from the sides of the bowl while it is being kneaded and when the dough feels tacky, not sticky, when you poke it. The dough should also pass the windowpane test, which means you can stretch out the out a piece of the dough and light can pass through it without it ripping. (If measuring by cups, be sure to fluff up the flour and spoon it into the measuring cups for a more precise measurement.)
   370 grams bread flour
5. Continue to knead the dough for 5 more minutes at medium speed.
6. Remove the dough and place it in a lightly greased straight-edge bowl. For the first rise, cover the bowl with the plastic cover or plastic wrap and let the dough rest in a warm spot to double in size.

   In my 70 degree F kitchen this took about 6-7 hours. The rise times can vary depending on the temperature of your kitchen. The warmer your kitchen, the faster the dough will rise. The opposite is true for cooler kitchens.

   I love this straight-edge bowl as it allows me to clearly see when the dough is done rising.

*See Notes below for Make-ahead options*

SHAPE

1. Once the dough has doubled in size, remove the dough onto a clean work surface. With a rolling pin, shape the dough into a 16 inch by 12 inch rectangle.
2. Spread the softened butter over the entire surface of the sourdough cinnamon roll dough. 
   57 grams unsalted butter, softened
3. In a small bowl, stir together dark brown sugar and ground cinnamon.

   Light brown sugar can be substituted for dark brown sugar.
   150 grams dark brown sugar, 12 grams ground cinnamon
4. Sprinkle the cinnamon sugar mixture on the entire surface of the dough. 
5. Starting at the long end closest to you, roll up the homemade cinnamon rolls into a long snake. Cut off the uneven edges, then divide into 9 equal pieces with unflavored dental floss, string, or a sharp knife. (about 1 3/4 inches per roll)

   Or, using a pizza cutter, slice the dough into 9 even stripes, then roll each into a roll for a more polished look. 
6. Grease an 9 x 9 inch baking dish, 2 quart baking dish or large cast iron skillet with butter before gently placing the Sourdough Cinnamon Rolls inside, about 1/2 - 1 inches apart.
7. Cover with plastic wrap and let rise for a second time until they have noticeably grown and look puffy.

   This took about 3-4 hours in my 70 degree F kitchen.
8. Not ready to bake these in the same day? No worries! See directions in the Notes below.

BAKE

1. Preheat the oven to 350 degrees F. Just before baking, pour warmed heavy cream over the Sourdough Cinnamon Rolls.

   The extra moisture from the heavy cream will keep the cinnamon rolls extra soft while baking.
   120 grams heavy cream, warm (just before baking)
2. Bake the Sourdough Cinnamon Rolls for 30-35 minutes or until the tops are golden brown and the internal temperature is 190 degrees F. 

   If the cinnamon rolls are browning too quickly, cover them with aluminum foil and continue baking.
3. Remove from the oven and place the cinnamon rolls on a wire rack to cool slightly.

Cream Cheese Frosting

1. While the cinnamon buns are cooling, prepare the cream cheese frosting.
2. In a large mixing bowl, mix unsalted butter and room-temperature cream cheese until combined. Add powdered sugar and heavy cream and blend until smooth. 
   28 grams unsalted butter, room temperature, 55 grams cream cheese, room temperature, 15 grams heavy cream, 90 grams powdered sugar
3. Using an offset spatula, spread the cream cheese frosting over the warm cinnamon rolls so that it can slightly melt into all of the cracks and crevices. Serve warm and enjoy!