Prepare Biscuits:
Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
In a large bowl, whisk together flour, baking powder, baking soda, sugar, and salt.
Cut in cold butter using a pastry cutter or your fingers until mixture resembles coarse crumbs.
Stir in cold buttermilk until dough just comes together. Do not overmix.
Shape Biscuits:
Turn dough onto a floured surface and gently pat to 1-inch thickness.
Use a biscuit cutter or glass to cut rounds. Place biscuits on prepared baking sheet, slightly touching for soft sides or spaced apart for crisp edges.
Bake Biscuits:
Bake for 12–15 minutes, until golden brown. Remove from oven and let cool slightly.
Prepare Sausage Gravy:
In a large skillet over medium heat, cook crumbled sausage until browned and cooked through, about 6–8 minutes.
Sprinkle flour over sausage and stir for 1–2 minutes to cook out the raw flour taste.
Gradually whisk in milk, ensuring no lumps. Simmer for 5–7 minutes until thickened, stirring frequently.
Season with salt, black pepper, and red pepper flakes if using. Adjust consistency with more milk if necessary.
Serve:
Split biscuits in half and spoon warm sausage gravy over the top. Serve immediately.