Preheat the oven to 450°F (230°C).
In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
Cut in the cold butter using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
Pour in the buttermilk and stir just until combined; do not over-mix.
Turn the dough out onto a floured surface and gently pat it into a rectangle about 1-inch thick.
Cut out biscuits using a biscuit cutter or a glass; place them on a baking sheet.
Bake in the preheated oven for 12-15 minutes, or until golden brown.
Prepare the sausage gravy while the biscuits bake. In a skillet over medium heat, cook the sausage until browned, breaking it up as it cooks.
Sprinkle the flour over the cooked sausage and stir to combine, cooking for another minute.
Slowly add the milk while stirring constantly to avoid lumps; bring to a simmer.
Season the gravy with salt, pepper, and optional cayenne to taste; cook until thickened.
Serve the hot biscuits topped with the sausage gravy.