Combine the warm water, milk, yeast, and sugar. Let proof for 5 minutes.
In a large bowl, combine flours and salt. Using your fingers, crumb the butter with the flour.
In a small bowl, beat one egg. Add the beaten egg, and yeast mixture, to the flour. Using a dough scraper, combine until the dough holds together.
Turn the dough out onto a floured surface and knead until smooth – about 10 minutes. Be vigorous – throw it down onto the counter every few kneads. Add flour as needed, but keep in mind that more flour will result in a tougher bun.
Place in a lightly oiled bowl and cover to let rise until doubled in size – 1-2 hours. Remove the dough from the bowl, shape into a rectangle, and cut into 8 equal pieces.
Place on parchment paper and cover with a light tea towel or oiled plastic wrap, and allow to rise another 1-2 hours – until doubled in size again.
Preheat the oven to 400 F.
Bake until golden on top, 13-15 minutes. Let cool completely before cutting and using for burgers.
Notes
I threw in about ⅓ cup of ground flax for this batch as well, as I was slightly short on whole wheat flour.
Recipe by The Kitchen Paper at http://c02.ddd.mwp.accessdomain.com/rustic-wheat-burger-buns/