Preheat oven to 425°F. In a mixing bowl, whisk together flour, baking powder, baking soda, and salt. Cut in cold butter using a pastry cutter or fork until mixture resembles coarse crumbs with pea-sized butter pieces.
Stir in cold buttermilk until dough just comes together - don't overmix. Turn dough onto a floured surface and gently fold a few times. Roll to 1-inch thickness and cut into rounds with a biscuit cutter. Place on a baking sheet.
Bake for 12-15 minutes until golden brown on top. The biscuits should be fluffy and cooked through.
While biscuits bake, shape breakfast sausage into patties slightly larger than the biscuits (they'll shrink during cooking). Cook in a skillet over medium heat for 3-4 minutes per side until browned and fully cooked through. Drain on paper towels.
Split warm biscuits in half horizontally. Place a sausage patty inside each biscuit. Add a slice of cheese if desired while the biscuit and sausage are still warm so it melts slightly.
Top with the other biscuit half and serve immediately while hot. These are best enjoyed fresh and warm.
