Make dough. In a large mixing bowl, add the milk, sugar, salt, butter, and the active sourdough starter. Mix everything together with a whisk or bread whisk. Next, mix in 1 cup of bread flour. Then add the rest of the bread flour and mix everything together to form dough.
Rest. Let the dough sit, covered, for 30 minutes. The dough will be pretty sticky, but this is normal.
Stretch and folds. Wet your hands with water (to prevent the dough from sticking to your hands) and grab one section of the dough. Stretch the dough out and fold it over. Turn the bowl by ⅓ and repeat two more times, getting all sides of the dough. Flip the dough over, cover the bowl, and let it sit for 30 more minutes. Repeat the stretch and folds process two more times for a total of 3 stretch and folds sessions.
Overnight rise. After the three stretch and folds, let the dough rise overnight for 10-16 hours, until it is doubled in size. Keep in mind that the rise time can vary depending on the temperature of your kitchen.
Shape. Grease a 9x13 casserole dish with some baking spray. Using the all-purpose flour, dust your working surface and turn the dough out onto the floured surface. Separate the dough into 12 equal parts and shape them into balls. You will want to use some of the all-purpose flour to help prevent the dough from sticking to your hands.
Second rise. Place the 12 dough balls into the prepared baking dish. Brush the top of the rolls with some egg wash, cover, and let them rise for 30 minutes to 1 hour in a warm place.
Bake. Preheat the oven to 375℉ and bake for 30 minutes or until golden brown. Remove from the oven and let them cool for 20 minutes before serving.
Notes
You can shape the rolls and do the second rise in the fridge overnight. Let them come to room temperature before baking.