Preheat oven to 450°F; line a baking sheet with parchment.
Whisk flour, baking powder, sugar, and salt in a large bowl for biscuits.
Cut in cold butter with a pastry cutter or fork until coarse crumbs form.
Make a well; add buttermilk and stir just until dough comes together without overmixing.
Gently pat dough on a floured surface to 3/4-inch thick; cut with a 3-inch cutter.
Place biscuits on sheet; bake 12-15 minutes until golden brown.
Meanwhile, brown sausage in a large skillet over medium-high, crumbling, for gravy.
When cooked through, sprinkle flour over sausage; stir and cook 1-2 minutes.
Gradually add milk, stirring constantly to prevent lumps.
Simmer 5-7 minutes, stirring frequently, until thickened.
Season with salt and pepper to taste.
Split warm biscuits; cover generously with hot gravy and serve immediately.