In a large high-sided skillet or a dutch oven, brown the sausage over medium-high heat, breaking it up as it cooks.
Add the butter and onion, cooking over medium heat until the onion is translucent, 3-4 minutes. Add the garlic and cook for 1 more minute.
Sprinkle the flour all over the sausage mixture and stir to coat all of the ingredients. Cook for 1-2 minutes, stirring constantly. Slowly add the milk, followed by the dried sage; cook, stirring constantly, until the mixture comes to a simmer and starts to thicken. Let simmer for a few minutes until thick and creamy. Taste and season with salt and pepper as desired.
Serve warm over biscuits.
Notes
You can use mild, medium, or hot sausage in this recipe.For a thinner gravy, add more milk a splash at a time to reach your desired consistency.Store gravy in an airtight container in the refrigerator for up to 3 days or in the freezer for up to 3 months (thaw in the refrigerator overnight). Reheat in a saucepan over low heat. Add a few splashes of milk to thin out the gravy if needed after reheating.