1) Preheat the oven to 425°F. Lightly grease a baking sheet, or line it with parchment paper.
2) Whisk together the flours, buttermilk powder, baking powder, and salt in a large mixing bowl.
3) Cut the butter into pats, then work it into the dry ingredients to form coarse crumbs. Toss in the nuts.
4) Whisk together the egg and milk. Add to the flour mixture and blend lightly until the dough is evenly moistened. Add a tablespoon or so additional milk to incorporate any extra flour in the bottom of the bowl.
5) Turn the dough onto a floured work surface and use a bench knife or bowl scraper to fold it over on itself three or four times, until it comes together.
6) Pat the dough into a 1"-thick circle. Use a 2" biscuit cutter to cut rounds. Pat the scraps together, and cut additional biscuits.
7) Transfer the biscuits to the prepared pan. Brush the tops with milk.
8) Bake the biscuits for 14 to 16 minutes, until they're golden brown. Remove them from the oven and serve warm.
Yield: 1 dozen biscuits.