This is the gravy that one of my granddaughters always wants for breakfast when she's visiting. Today was the first time that I've ever measured the ingredients for it. Start with the smaller amounts of salt and pepper, taste and then add more until it's to your liking. You can always add more, but you can't remove it. Serve over biscuits, toast, grits or scrambled eggs.
In a large nonstick or well-seasoned cast iron skillet, add and melt sausage grease over low heat.
Stir in flour and mash the grease into it (the flour will still be very dry.)
Add 1/2 cup milk and stir well, mashing lumps until smooth (about 1-2 minutes.)
Stirring, gradually add remaining 4 cups milk and stir until smooth.
Add salt and pepper.
Stirring constantly, increase heat to medium-high and bring to simmer-low boil.
Reduce heat to medium-low and continue stirring, concentrating on the bottom of the skillet, until gravy is thickened to desired consistency (at least 1 1/2 to 3 minutes. If it begins to stick to the bottom, remove from heat and stir, scrape and blend; return to lower heat.)
Crumble or tear cooked sausage into gravy, stir and taste for seasoning, adding more to taste.
Remove from heat and serve immediately.
Keep pan covered with lid or foil to prevent a "skin" from forming on top.
Refrigerate leftovers in an airtight container.
NOTE: I usually cook a whole pound of sausage and use 2 or 3 pieces for the gravy. If you don't have the grease, you may use butter, bacon grease or lard.