Combine warm water, warm milk, yeast and sugar in small mixing bowl and let stand until foamy (about 5 minutes)

In large mixing bowl, add flour, salt and butter and mix until butter resembles crumbs. Stir in yeast mixture and beaten egg until dough forms.

Turn dough on to well-floured surface and knead for about 12−15 minutes (if using stand mixer with dough hook, mix 8−10 minutes). Return dough to bowl; cover with damp kitchen towel. Allow dough to rise in warm place until doubled in size, 1−2 hours.

Punch down dough and divide into 12 equal parts. Roll dough into tight balls, place seam side down on a parchment-lined baking sheet. Cover loosely with towel; allow to rise for 1−2 hours, or until doubled in size again

Preheat oven to 400 degrees.

Brush each bun with egg yolk; if yolk is too thick, thin with a few drops of water or cream. Sprinkle with sesame seeds, if desired.

Bake for 15−20 minutes on center rack until dark golden brown. Transfer to wire rack to cool completely

Slice in half, fill with your favorite filling and enjoy!