In a large skillet with deep sides, over medium-high heat, add the sausage. Brown and crumble the sausage, stirring occasionally until cooked through and there is no pink left, about 5 minutes. You will not drain the excess grease.
Turn the heat to medium-low. Add the butter to the pan, stir it in to melt.
Add the flour and stir it in so it gets absorbed in the fat and covers the sausage. Cook for 30 seconds, stirring constantly.
Very slowly stream in the milk while stirring constantly. If you pour the milk in too fast it may form lumps. Continue to cook, stirring occasionally until it comes to a simmer and thickens, 3-5 minutes.
Make sure to scrape the bottom and corners of the pan where the flour mixture may get stuck.
Season with the black pepper and pepper flakes, if using, stir it in. Taste and adjust seasoning if necessary. I usually find I need to add a bit more salt.
Serve over your favorite biscuits.
I like to use spicy pork sausage, and trust me, I don't handle spice well at all so it's not what I would consider spicy at all. I've made it with sage sausage and just regular mild sausage. I find the spicy pork sausage gives it just a little bit of kick to really add flavor but not enough that you need to drink a glass of milk to cool the flames.
I know some of you love it really spicy. If you do, definitely add the red pepper flakes (but they are optional.)
If you want a quick biscuit recipe to serve this gravy with, try my recipe for BUTTER DIP BISCUITS.
Whole milk is the best for this gravy recipe as it makes it nice and thick but you can use any milk that you have. But if you are going to go through the trouble of making the best gravy ever, you really need to go with the full fat milk for the best flavor.
I cannot tell you about any milk, flour or meat substitutions for this recipe. I only make it this way and any substitutions will alter the taste and texture of this gravy.
Make sure that the flour is soaked up by the fat from the sausage as much as possible before adding milk. Do not add all the milk at once. Slowly stir it in. This helps prevent any lumps to form so you will have a smooth gravy.