Heat up the refried beans in a large pan. Add in the vegetable stock, water and tomato paste and blend until smooth. You want the sauce to be very thin, so add more liquid if necessary. If the sauce is too thick it will weigh down the tortillas and tear them. Using tongs, take a tortilla and dip in the sauce. This is a bit of an art—you want them to soak through enough that they are pliable and won’t tear, but soak them for too long and they’ll come apart when you lift them out.

Lay the tortilla dipped in bean sauce flat in a small baking dish. Sprinkle some cheese on one side of the tortilla, and then fold it in half like a quesadilla. Repeat this with each tortilla until the baking dish is full. Pour the remainder of the bean sauce into the pan and sprinkle with remaining cheese.

Bake at 350ºF for about 10 to 15 minutes, or until the cheese has melted.