Step 1: Prepare the Fluffy Biscuits

1. Preheat Oven and Prepare Baking Sheet: Preheat your oven to 450°F (232°C). Line a baking sheet with parchment paper or lightly grease it.
2. Combine Dry Ingredients: In a large bowl, whisk together the flour, baking powder, salt, and baking soda. Whisking ensures the leavening agents and salt are evenly distributed throughout the flour.
3. Cut in Cold Butter: Add the cold, cubed butter to the dry ingredients. Using a pastry blender, your fingertips, or two knives, cut the butter into the flour mixture until it resembles coarse crumbs with some pea-sized pieces of butter remaining. The goal is to keep the butter cold and in small pieces, which will create flaky layers in the biscuits. Work quickly to prevent the butter from warming up too much.
4. Add Buttermilk: Make a well in the center of the dry ingredients and pour in the cold buttermilk. Stir with a fork or spatula just until the dough comes together. Do not overmix! Overmixing will develop gluten and result in tough biscuits. The dough will be shaggy and slightly sticky, and that’s okay.
5. Turn Dough onto Floured Surface and Knead Gently: Lightly flour a clean work surface. Turn the dough out onto the floured surface. Gently knead the dough 4-5 times, just until it comes together into a slightly smoother ball. Over-kneading will make the biscuits tough.
6. Pat or Roll Dough to Desired Thickness: Pat or gently roll the dough to about 3/4 to 1 inch thickness. Thicker biscuits will be taller and fluffier. Thinner biscuits will be crisper and less fluffy.
7. Cut Out Biscuits: Use a 2-3 inch biscuit cutter (or a sharp knife to cut squares) to cut out biscuits. Press straight down with the cutter; do not twist, as twisting can seal the edges and prevent them from rising properly. For softer-sided biscuits, place them close together on the baking sheet. For crispier-sided biscuits, space them further apart.
8. Bake Biscuits: Place the baking sheet in the preheated oven and bake for 12-15 minutes, or until the biscuits are golden brown on top and cooked through. The baking time may vary slightly depending on your oven and the thickness of the biscuits.
9. Serve Warm: Remove the biscuits from the oven and let them cool slightly on the baking sheet or a wire rack. Serve warm, preferably immediately, with sausage gravy.

Step 2: Prepare the Rich and Creamy Sausage Gravy

1. Brown the Sausage: In a large skillet or Dutch oven over medium-high heat, crumble the breakfast sausage and cook, breaking it up with a spoon, until it is browned and cooked through. Drain off any excess grease, leaving about 2 tablespoons of grease in the skillet for flavor. Leaving some grease is essential for flavor and for creating a roux, which is the base of the gravy.
2. Add Flour and Cook Roux: Reduce the heat to medium-low. Sprinkle the flour over the cooked sausage in the skillet. Cook, stirring constantly with a wooden spoon or whisk, for 1-2 minutes, or until the flour is lightly golden and fragrant. This process creates a roux, which is a mixture of fat and flour used to thicken sauces and gravies. Cooking the roux removes the raw flour taste and ensures a smooth gravy.
3. Gradually Whisk in Milk: Gradually whisk in the milk, about 1/2 cup at a time, whisking constantly to prevent lumps from forming. Start with a small amount of milk and whisk until smooth before adding more. This gradual addition helps to create a smooth and lump-free gravy.
4. Simmer and Thicken: Increase the heat to medium and bring the gravy to a simmer, stirring occasionally. Reduce the heat to low and simmer gently for 5-7 minutes, or until the gravy has thickened to your desired consistency. The gravy will thicken as it simmers and the starch in the flour gelatinizes. If the gravy becomes too thick, you can thin it out with a little more milk or chicken broth.
5. Season and Finish: Stir in the salt, black pepper, thyme (if using), and red pepper flakes (if using). Taste and adjust seasoning as needed. You may need to add more salt or pepper to taste. Simmer for another minute or two to allow the flavors to meld together.
6. Serve Hot: Serve the sausage gravy hot over warm biscuits.