Preheat the oven to 425 degrees F. Line a baking sheet with parchment paper.
Whisk together both flours, the baking powder, sugar, 1/2 teaspoon salt and 1/4 teaspoon pepper in a large bowl. Work in the butter using your fingers or a pastry cutter until the mixture resembles small peas.
Add the milk and stir until just incorporated. Gently knead into a ball, and then pat into a 1-inch-thick rectangle. Cut into twenty-four 1 1/2-inch squares and place on the prepared baking sheet, leaving about 1 inch between each biscuit. Sprinkle an additional 1/4 teaspoon salt and pepper on top.
Bake until golden brown, about 20 minutes. Cool on the baking sheet and serve warm.