1. Whisk starter/discard, warm milk, egg, butter, and sugar until smooth; add flour and salt and mix until no dry spots remain.

2. Knead 8–10 minutes (mixer on low) or 10–12 minutes by hand until smooth, elastic, and slightly tacky; dough should pass a windowpane test.

3. Place in a lightly oiled bowl, cover, and bulk ferment at room temp until doubled, 3–5 hours (longer if using discard or a cool kitchen).

4. Turn dough onto a lightly floured surface and divide into 8 equal pieces; shape each into a tight ball by tucking edges under.

5. Arrange on a parchment-lined sheet pan, spacing 2–3 inches apart; cover loosely and proof until puffy and nearly doubled, 1.5–2.5 hours.

6. Near the end of proofing, preheat oven to 375°F (190°C).

7. Brush buns with egg wash; sprinkle sesame or seasoning if desired.

8. Bake 18–22 minutes until deep golden and an internal temp reads 190–195°F (88–90°C).

9. Cool on a wire rack completely for a set, fluffy crumb.

10. Serve fresh or store airtight up to 3 days; freeze up to 3 months and rewarm at 300°F (150°C) for 8–10 minutes.