Give the yeast a few minutes to dissolve completely. Stir in the sourdough starter until the starter is mostly dissolved (a few stringy bits are ok). Add 4 cups of the flour and the salt, and stir to make a shaggy dough. With the dough hook attachment and your mixer on low speed, knead the dough for about 8 minutes.ive the yeast a few minutes to dissolve completely. Stir in the sourdough starter until the starter is mostly dissolved (a few stringy bits are ok). Add 4 cups of the flour and the salt, and stir to make a shaggy dough. With the dough hook attachment and your mixer on low speed, knead the dough for about 8 minutes.