In the bowl of a stand mixer fitted with a dough hook, combine the flour, dry milk powder, sugar, salt, and yeast. Stir to combine.
2¾ cup all-purpose flour, ¼ cup non-fat dry milk powder, 2 tablespoon granulated sugar, 1½ teaspoon kosher salt, 2¼ teaspoon instant yeast
Add the eggs, egg yolk, and water. Mix on low speed until a shaggy dough forms.
3 large egg, 1 large egg yolk, ¼ cup water
With the mixer running on low speed, add the butter one tablespoon at a time, allowing each addition to fully incorporate before adding the next.
10 tablespoon unsalted butter
Once all the butter is incorporated, increase the speed to medium-high. Knead for 15-20 minutes, or until the dough becomes smooth, shiny, and begins pulling away from the sides of the bowl.
Transfer the dough to a lightly greased bowl using a rubber spatula, shaping it into a ball. Cover with plastic wrap or a plate, and let rise at room temperature for one hour.
Transfer the dough to the refrigerator and chill for at least eight hours or up to 12 hours.
Divide the dough into six equal portions, about 125 grams each.
Shape each portion into a tight ball using the cup-and-roll method. Fold the edges underneath, then roll the dough against a clean surface using your palm to create tension.
Place the dough balls onto a parchment-lined baking sheet. If using ring molds, place one around each dough ball. Cover loosely with plastic wrap.
Let the buns proof until very puffy, one to three hours depending on room temperature.
Preheat the oven to 375°F (190°C). While the oven preheats, transfer the buns to the refrigerator for a few minutes to firm slightly.
Whisk together the egg, egg white, and water for the egg wash. Brush over the buns and sprinkle with sesame seeds, if desired.
1 large egg, 1 large egg white, 1 tablespoon water, optional sesame seeds
Bake for 16-18 minutes, or until golden brown and the buns reach an internal temperature of 190°F (88°C).
Remove from the oven and let cool completely.