Dough ingredients: – all-purpose flour – active sourdough starter – milk – granulated sugar
In the bowl of a stand mixer, combine all the dough ingredients except for the butter. Mix on low speed until the flour is fully hydrated and no dry spots remain.
Once all the butter is added, slightly increase the speed and mix for about 20 minutes. The dough should be soft, smooth, and elastic—when gently stretched, it should pass the windowpane test.
Scrape down the bowl, cover it with a damp towel or plastic wrap, and let it rest for 30 minutes. Perform 2 to 3 sets of stretch and folds, spaced 30 minutes apart.
Let the dough rise at room temperature until it increases by about 50 percent in size. Then cover the bowl and refrigerate overnight.