Mix Dry Ingredients- In a medium mixing bowl, whisk together the flour, baking powder, baking soda, salt, and sugar. Cut 1 cup of butter into 1⁄8-inch thick pieces. Cut the butter into the flour mixture with your fingers or a pastry cutter, until it looks mealy in texture.
Add Buttermilk - Gradually add 1 cup buttermilk into the flour mixture, stirring with a fork until incorporated. If needed, add an extra 1 to 2 tablespoons so most of the flour is hydrated and can be kneaded into the dough.
Knead and Roll - Knead the dough in the bowl until it forms a mass, about 5 to 6 times. Lightly dust a working surface with the flour. Place the biscuit dough onto the floured surface. Lightly flour a rolling pin and roll the dough ¾-inch thick.
Cut the Dough - Using a 2 1⁄2-inch floured biscuit cutter, press straight down into the dough without turning. Transfer to a parchment paper–lined sheet pan and repeat with the remaining dough. Use the scraps to roll and cut more biscuits. Refrigerate for 30 minutes or freeze for 15 minutes before baking.
Bake - Set the oven rack to the lower-middle position and preheat to 450°F (232°C). Transfer the biscuits to a parchment paper–lined sheet pan at least 1 inch apart. Melt 2 tablespoons butter, then brush the tops of each biscuit and sprinkle with salt. Bake until golden brown, 10 to 11 minutes. Cool for 5 to 10 minutes before serving with the gravy.
Sausage Gravy
Cook the Sausage - Heat a large nonstick pan or skillet over medium heat. Add the pork sausage and break it into smaller pieces using a spoon. Cook until no longer pink and lightly browned, about 5 to 6 minutes.
Cook the Aromatics - Melt the butter in the pan. Add the onions, garlic, and thyme. Cook until fragrant and onions are tender, 1 to 2 minutes.
Cook the Flour - Sprinkle the flour, salt, and pepper over the sausage mixture. Stir and cook until the flour is absorbed, about 2 minutes.
Add the Milk - Slowly stir in the milk, then turn up the heat to medium-high to bring to a boil. Reduce the heat to a simmer, cook, and stir occasionally until the gravy is thick and can coat the back of a spoon, about 5 minutes. Add more salt and pepper to taste.
To Serve - Serve with biscuits split in half or kept whole with sausage gravy on top.
Notes
Serving Size: 1 biscuit with gravy
Storing: Store biscuits in an airtight container for up to 5 days, or wrap and freeze for up to 1 month. Refrigerate the gravy for up to 5 days.
Make it Gluten-Free: Substitute gluten-free flour for all-purpose flour for the biscuits. I recommend Bob's Red Mill 1:1 Baking Flour. For the gravy, substitute the flour with 2 tablespoons of cornstarch mixed with 1/4 cup of water. Mix into the simmering milk, stirring until thickened.