While the biscuits are baking...In a large skillet or dutch oven, brown the sausage.
When the sausage is cooked, add flour until it soaks up the grease and the sausage looks matte - maybe 1 cup flour?
Cook the flour and sausage for a couple minutes. (If you like a brown colored gravy, cook until the flour is brown. Otherwise, just cook a couple minutes.)
Add most of the milk and season with garlic salt, black pepper, and salt.*A secret ingredient that adds another dimension to gravy is a little chicken boullion.
Simmer on med/low until serving time. If the gravy gets too thick, add a little more milk and seasonings.