Step 1

In a small saucepan, scald the milk (Scalding is heating until small bubbles form around the edges of the pan and steam rises from the surface, but never boiling).

Step 2

Remove the milk from the heat, and then add the water. Stir, and let sit until it registers about 105-degrees F.

Step 3

Once the milk-water mixture is the right temperature, stir in the yeast and a pinch of the sugar. Let the yeast mixture bloom, about 5 minutes. It should be foamy on the surface.

Step 4

To the milk and yeast mixture, stir in the butter and egg. (Don't worry if the butter doesn't melt all the way immediately).

Step 5

In a mini stand mixer fitted with the dough hook, add the liquid ingredients, and beat briefly to combine.

Step 6

In a small bowl, whisk together both flours with the salt and tablespoon of sugar.

Step 7

While the mixer is running, add the dry ingredients in two batches.

Step 8

Crank the mixer to medium-high, and knead for 8-10 minutes. The dough will be sticky.

Step 9

Place the dough in a well-oiled bowl, turning it to coat with oil. Cover loosely with plastic wrap, and then let rise in a warm place for about 2 hours, or until doubled. (Rising time is dependent on the temperature of the room; let rise until the dough is doubled).

Step 10

Punch the dough down very well, and gather it into a ball.

Step 11

Weigh the dough, and divide it by 4--each dough ball should be between 95 and 97 grams.

Step 12

Roll each dough piece into a ball, and then use your fingers to pinch the edges under until the seam is on the bottom (see photo for reference). Then, cup your hand over the dough ball on the counter, and make circles on the counter with the dough to roll it into a perfect ball.

Step 13

Repeat with the other 3 pieces of dough.

Step 14

Place the 4 dough balls on a baking sheet, and cover loosely with plastic wrap. Place in a warm place to rise for 1 hour. They will be puffy when ready.

Step 15

Meanwhile, preheat the oven to 375.

Step 16

Finally, make the topping: whisk the egg yolk with a splash of water. Brush generously on each bun, covering the entire surface, and then sprinkle with sesame seeds.

Step 17

Bake for 16-19 minutes, until deeply golden brown.