Create an active sourdough starter

1. In the morning, feed your sourdough starter by adding 1/3 cup of all purpose flour to an existing 1/3 cup of starter, and enough water to make a thick batter, similar in texture to muffin batter, or very thick pancake batter. 
2. Set in a warm place, loosely covered until starter peaks. This should take 4-6 hours.
3. Stir dough starter, and measure out 1/3 cup for your recipe, put a lid on the rest, and place in the refrigerator until needed again. 

Make the dough

1. Melt butter
2. In the bowl of a stand mixer, combine flour and salt
3. Add egg, milk, sourdough starter, and butter, and mix with dough spiral until a ball of dough forms
4. Continue kneading dough for about five minutes, until the ball has smoothed out, and is no longer shaggy
5. Cover, and allow to proof at room temperature for 4-5 hours, then place in the refrigerator overnight 

Make the rolls

1. In the morning, remove dough from refrigerator
2. Melt butter for the filling, and set aside
3. Combine cinnamon and brown sugar in a smaller bowl, and set aside
4. Dump ball of dough from bowl onto a clean, smooth surface. If your dough is properly kneaded, you shouldn’t need to use any flour to dust the surface, but if not, no worries! sprinkle a little flour on the counter top, as well as onto your rolling pin as needed
5. Roll dough into an 18×10 inch rectangle
6. Brush with melted butter, then sprinkle with cinnamon sugar
7. Roll dough along the short side (making a long, skinnier log, rather than a shorter, fatter one)
8. Cut into 12 1 1/2 inch rolls
9. Arranged in a greased 9×13 inch baking pan
10. Cover, and allow to proof in a warm place for about 30 minutes
11. Preheat oven to 350º
12. Bake rolls for 25-30 minutes, until they begin to turn golden on top

Optional: ice rolls with your preference of frosting after rolls have cooled enough to handle