You can make your own soup concentrate, basically you make a white sauce.
Melt butter then stir in flour, forming a roux. Once it browns you slowly stir in milk or cream. Then you can add cooked mushrooms and onions, cheese, or whatever flavorings your soup needs. Salt or season and ta-da! you're done.
It might be a little bit more wet than a can of soup. If you cook it longer, it will condense down more. I can't remember if there's a recipe for that in NT. It doesn't use much flour, anyway (maybe Sally would use arrow root to thicken?).