In the bowl of a stand mixer, combine the warm water, warm milk, sourdough starter, egg, honey, and olive oil. Add the freshly milled flour and salt. Mix until a shaggy dough forms, then knead until the dough starts looking smoother and more elastic, about 5-10 minutes. Fresh milled dough often looks rough at first, so don’t worry if it takes a little time. We’re not looking for the dough to come into a ball, and we’re not chasing the windowpane. All we’re doing here is mixing the dough really well and giving the gluten development a jump start. Transfer the dough into the bowl that you plan to bulk ferment the dough in. Cover the dough and let it rest for 30 minutes.

During the first 2 hours of bulk fermentation, perform 2 sets of stretch and folds, spacing them about 30–45 minutes apart. The dough should gradually become smoother and easier to handle.

Continue bulk fermentation until the dough looks puffy and has risen noticeably. Depending on your kitchen temperature and starter strength, this can take about 5–8 hours.

Divide the dough into 8 equal pieces (or 10, if you want slightly smaller ones). Shape each piece into a smooth ball by gently pulling the outer surface underneath to create tension on top.

Transfer the buns to a parchment-lined baking sheet, leaving some space between them.Cover the buns and let them rise for about 2–4 hours, or until they look a bit more puffy and soft.

Near the end of the second rise, preheat the oven to 175°C (350°F). Whisk together the egg and milk for the egg wash. Gently brush the tops of the buns and sprinkle with sesame seeds if desired.

Bake for 20–25 minutes, or until golden brown and the internal temperature reaches about 88°C (190°F).

Let the buns cool before slicing. They become even softer as they cool.