Prepare the Sourdough Starter:
Feed your sourdough starter the night before to ensure it’s bubbly and active.
Mix the Dough:
Combine sourdough starter, flour, water, sugar, egg, salt, and butter in a mixing bowl. Stir until a shaggy dough forms. Let it rest for 30 minutes.
Stretch and Fold:
Perform three sets of stretch and folds over 90 minutes, at 30-minute intervals. Cover and let the dough rise until doubled in size (4-6 hours at 72°F).
Shape the Buns:
Turn the dough onto a floured surface and divide it into 6 equal portions (about 115g each). Shape into round buns and place on a parchment-lined baking sheet.
Second Rise:
Cover the buns with a kitchen towel and proof for 1-2 hours, until puffy.
Preheat and Prepare:
Preheat your oven to 375°F (190°C). Brush the buns with egg wash and sprinkle with sesame seeds if desired.
Bake:
Bake for 18-20 minutes, or until golden brown. Let cool before serving.