Step 1

Pour the water and milk into a 2-cup glass measure. Microwave until the liquids achieve 105-110°F -- 30-45 seconds. Whisk in the yeast and sugar. Let sit until the mixture foams -- 5-10 minutes.

Step 2

In the bowl of the standing mixer, whisk together the flours and salt. Then add the butter, and rub it between fingers until the flour turns slightly crumbly -- about 1 minute. Add the yeast mixture and the beaten egg.

Step 3

Using the dough hook attachment, knead the dough at low or medium-low speed for a full 10 minutes. Then scrape the dough (it will be sticky) onto a non-floured surface and knead it a few times by hand. Grease or dampen your hands if the dough is too sticky to knead.

Step 4

Form the dough into a ball. Then drop the dough, smooth side down, into a large, greased bowl. Invert the dough to grease the other side. Cover the bowl with cling film, and then place the bowl in a warm location until the dough doubles in volume -- 90 minutes to 2 hours.

Step 5

Punch down the dough to deflate it. Put the dough on a non-floured surface, and cut it into 8 equal pieces. Form each piece into smooth-topped ball (see video), and place on a large parchment- or silicone mat-lined baking sheet. Cover loosely with greased cling film.

Step 6

Immediately place a pan of water on the bottom of the oven. Heat the oven to 400°F. In about 30 minutes, the water will achieve a boil and fill the oven with steam.

Step 7

Just before baking, brush the buns with the egg-wash and sprinkle on the poppy or sesame seeds.

Step 8

Bake the buns in the humid oven until they puff fully and color deeply -- about 18 minutes. Cool to room temperature before slicing.