Step 1

Crack 2 large eggs into the bowl of a stand mixer. Separate the last egg, adding the yolk to the stand mixer; cover and refrigerate the white. Cut 12 tablespoons (1 1/2 sticks) unsalted butter into 12 pieces. Let the eggs in the bowl and butter sit at room temperature until the butter is softened, 1 to 1 1/2 hours.

Step 2

Heat 2/3 cup of the whole milk in the microwave until warm (120°F to 130°F), about 45 seconds. Pour over the eggs. Add 3 cups bread flour, 3 tablespoons granulated sugar, 3 1/2 teaspoons instant yeast, and 2 1/4 teaspoons kosher salt. Mix with the dough hook attachment on the lowest speed until a shaggy dough forms, about 2 minutes. Increase the speed to medium-low and knead until the dough forms a ball that’s beginning to get smooth, about 2 minutes.

Step 3

With the mixer still on medium-low speed, add the butter a piece at a time, waiting for each piece to be incorporated before adding the next. Increase the speed to medium and mix until the dough is smooth, elastic, and passes the window test, about 8 minutes. To do the window test, pinch off a small piece of dough and use your fingers to gently stretch it as thin as possible without tearing. If you can stretch the dough thin enough to see light shine through, it passes the test.

Step 4

Lightly coat a large bowl with neutral oil. Gather the dough into a ball. Place in the bowl and turn to coat. Cover the bowl with plastic wrap and refrigerate until about doubled in size, at least 12 hours and up to 18 hours.

Step 5

Line 2 baking sheets with parchment paper. Turn the dough out onto a lightly floured work surface. Divide the dough into 8 pieces with a bench scraper or knife. Cover with plastic wrap to keep from drying out.

Step 6

Shape the buns one at a time: Pull the corners of a piece of dough into the center. Flip the dough over so that the smooth side is facing up. Cup a hand around the dough and roll the dough in a circular motion against the work surface to round and seal the bottom seam.

Step 7

Place 4 buns on each baking sheet, spacing them evenly apart. Loosely cover with plastic wrap and let rise in a warm place until doubled in size, 1 1/2 to 2 hours. If it slowly springs back when poked but holds an indent, it’s ready.

Step 8

When the dough is almost ready, arrange 2 racks to divide the oven into thirds and heat the oven to 375°F. Add the remaining 1 1/2 teaspoons whole milk to the reserved egg white and whisk to combine.

Step 9

Unover the buns and gently brush with the egg wash. Sprinkle with 2 tablespoons sesame seeds if desired.

Step 10

Bake for 8 minutes. Rotate the baking sheets from front to back and top to bottom and bake until deeply golden brown, 5 to 8 minutes more. A thermometer inserted into the center should register at least 190°F, and the bottom will sound hollow when tapped. Let the buns cool for 5 to 10 minutes on the baking sheets. Transfer to a wire rack to cool completely.