For mushroom, you'd fry some mushrooms and onion in a couple of tablespoons of marge, add 3 tablespoons of flour, stir it all around for a minute or so to get the flour granules all greasy and separated, then add 12 oz / 340 g of your preferred style of milk along with your choice of seasoning (salt, pepper allspice, thyme--that's what I'd put in). Stir it all as you let it heat up to a simmer and thicken.

"Cream of..." soups (the canned kind used as ingredients are what I'm talking about here) are easy to make - you just make a thick white sauce with the featured ingredient incorporated.