In a medium mixing bowl, whisk together the warm water, milk, yeast and sugar, then beat in the eggs.

In the bowl of a stand mixer fitted with the paddle attachment, add the flours, salt and butter. Mix on low for 1 minute. Pour in yeast mixture into the bowl of the stand mixer.

Switch to the dough hook. Turn mixing speed on medium for 7-9 minutes until a soft, sticky dough forms.

Shape the dough into a ball, then cover the bowl with a damp kitchen towel and let it rise until doubled, this can take anywhere from 1- 3 hours depending on the temperature and humidity in your house. Keep an eye on it after the hour mark.

Line a baking sheet with parchment paper or a baking mat. Punch the dough down and divide the dough into 8 equal pieces (you can use a kitchen scale to be exact).

To shape the dough, flatten each piece, then gather the ends and pinch the dough to seal in the center. Flip the dough over, cup the surface with your palm, and roll it into a ball. Place each ball of dough about 2 inches apart. Cover with a greased piece of plastic wrap or foil (this will prevent the dough from sticking to it). Rest in a warm place for 1 hour, or until puffy and slightly risen.

Preheat oven to 375 degrees.

To make the egg wash, in a small bowl, whisk the egg yolk with water. Brush generously on each bun, covering the entire surface, then sprinkle with sesame seeds, if desired.

Using a spray bottle or mister bottle, open your oven and spritz it several times (6 times or so with a big bottle, 10 times or so with a little bottle). Spritz the top of the buns with water. This will help prevent them from cracking, especially if you live in a dry climate. Place the buns in the oven and bake for 15-18 minutes or until they turn a deep golden brown. Remove from the oven and allow to cool on the sheets for 5 minutes before transferring them to a wire rack to cool completely.