For The Dough – all-purpose flour – active sourdough starter – milk
In a stand mixer bowl, combine the flour, sourdough starter, milk, sugar, egg, and salt. Mix on low until everything is combined.
Gradually add the butter, one tablespoon at a time. Let each addition mix in fully before adding more.
Increase the mixer speed and knead for about 20 minutes, until the dough is smooth and elastic.
Rest and Fold
Cover the dough and let it rest for 30 minutes. Perform 2–3 sets of stretch-and-folds every 30 minutes.
Bulk Fermentation
Let the dough rise at room temperature until it increases by about 50% in volume (about 6–8 hours at 72°F/22°C).