Step 1: Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.
Step 2: In a large bowl, whisk together 2.5 cups flour, baking powder, and salt.
Step 3: Add the frozen grated butter to the flour and toss to coat. Mix until the texture resembles coarse crumbs.
Step 4: Stir in the cold buttermilk until a shaggy dough forms. Do not overmix.
Step 5: Turn dough onto a floured surface, fold it over itself 5-6 times, then pat to 1-inch thickness.
Step 6: Cut biscuits with a 2.5-inch cutter and place on the baking sheet. Bake for 15-18 minutes until golden.
Step 7: In a large skillet over medium-high heat, brown the sausage until fully cooked. Do not drain the fat.
Step 8: Sprinkle 1/3 cup flour over the sausage and stir for 2 minutes to cook the flour.
Step 9: Gradually whisk in the milk, starting with 3 cups. Simmer until thickened, adding more milk if needed.
Step 10: Season heavily with black pepper and salt. Serve hot over split biscuits.