Place kidney beans in a large saucepan. Fill pan with water and bring gently to a boil. Remove saucepan from heat and let beans soak in hot water for 1 hour.
Drain, and simmer with finely chopped onion and garlic in salted water in a large casserole. After about an hour of cooking, taste them. If they are cooked, drain; if not, continue to simmer until they are tender, but do not let them burst. Drain.
Mix butter, flour, cumin powder and Mexican chili powder (a combination of powdered chilies, cumin seed, dried garlic and oregano) to a smooth paste. Combine cooked beans and chili paste in a saucepan. Add bouquet garni, beef stock, and salt and freshly ground black pepper, to taste, and simmer, stirring gently from time to time, for about ¾ hour, until sauce is smooth and rich. Remove bouquet garni. Serve immediately.