Heat a large skillet over medium-high heat. Add the sausage and break it up into small pieces with a wooden spoon. Cook for about 5 minutes, stirring frequently to scrape any brown bits from the bottom of the skillet, until the sausage is cooked through.
Reduce the heat to medium-low and sprinkle the flour all over the sausage. Stir to combine and cook for 1 minute, until the flour is fully absorbed.
While stirring constantly, gradually pour in the milk. Cook over medium-high heat, stirring frequently, until the gravy thickens and comes to a simmer. Reduce the heat to medium-low and cook for 5 to 7 minutes, stirring frequently, or until your desired consistency is reached.
Season the gravy with the pepper, red pepper flakes, if using, and salt to taste.
Serve immediately over buttermilk biscuits.
Video
Notes
If you prefer a thinner gravy, add additional milk after it has thickened in step 3.
Add herbs: After adding the milk, add up to 1 to 2 teaspoons of freshly chopped herbs or ½ teaspoon of dried herbs, such as thyme, chives, rosemary, or sage.
Control the saltiness: The sodium level of breakfast sausages can vary greatly. Wait until the gravy is finished cooking before seasoning with salt to taste. You can also add more black pepper if you like!
Serve immediately: Gravy starts to thicken pretty quickly as it sits, so it is best served nice and warm over warm biscuits.