Fry sausage in a large cast iron skillet or Dutch oven over medium heat
When sausage has just a little bit of pink but is mostly brown, add onion; cook until translucent and sausage is no longer pink
Stir in flour; mix until no more white from the flour is visible
Stir in milk, seasonings, Worcestershire sauce, and hot sauce / red pepper flakes; cook until gravy thickens (stir often) You may need need to reduce heat to low during the process
Notes
*If you cannot find sage sausage, just add 1-2 tsp of ground sage to the sausage as you are cooking it.Adjust seasonings as needed. The quantities listed are a good starting point. I typically add more based on my family's tastes.