4 cups unbleached all-purpose flour
2 cups white whole wheat flour
1/4 cup minced fresh rosemary
2 tablespoons baking powder
2 teaspoons coarse salt
1 teaspoon cracked black pepper
1 1/2 cups (3 sticks) cold butter, cut into 1/4-inch pieces
2 cups shredded sharp cheddar cheese
3 ounces prosciutto, finely chopped
2 1/4 cups cold buttermilk
Preheat the oven to 400Â°F with racks in the upper and lower thirds.
In a large bowl, whisk together the flours, rosemary, baking powder, salt, and pepper.
With a pastry blender or your fingers, cut in the butter until the mixture resembles coarse meal but with some large pieces of butter remaining.
Add the cheese and chopped prosciutto. Stir in the buttermilk just until the mixture forms a dough; it will be crumbly.
Turn out the dough onto a lightly floured work surface and knead quickly to incorporate any loose crumbs.
Pat the dough into a 12-inch square. Cut into twelve 3-inch squares and transfer to two ungreased baking sheets. Brush the top of each biscuit with a little buttermilk.
Bake for 30 to 40 minutes, until the biscuits are golden brown and cooked through. Rotate the baking sheets from top to bottom and front to back halfway through.