When I make gravy for roast or turkey, I use corn starch to thicken. I drain grease from pan, return any broth to pan. Put a couple heaping tablespoons of corn starch in a cup, add water and stir. Dump in pan, and then I add more liquid as I stir with a whisk. Once it starts bubbling, it gets a pretty clear color and will thicken. I add the liquid until it is the way we like it, medium thickness. For milk gravy, I leave about two or three tablesppons of grease and brown bitys in the pan, stir in a couple heaping spoons of flour, add milk, stir with a whisk,until bubbling, and add small amounts of milk or water to thin it to the right consistency. I think using the whisk is what really cuts down on any lumps, and constant stirring. . I've never had lumpy gravy , and my roast gravy is to die for!!LOL