I think we’re talking about different things, asparagus isn’t usually topped with sauce in the US so I’m not sure what you’re referring to. And cereals are usually eaten with milk

White gravy is basically just roux with pepper. You use the rendered fat (plus some butter) from the meat you’re cooking, add some flour, let it cook for a bit and then pour some milk in. Salt and pepper to taste, there ya go, white gravy