In a medium saucepan, saute the garlic, onion, and tomatillos in the oil. Stir in the flour and saute for a few minutes more. Add the chicken stock and stir until smooth. Add the chiles and simmer 30 minutes. Add the salsa jalapena and simmer 10 minutes more. Add salt to taste. Use to make Enchiladas Verde Con Queso (Green Enchiladas with Cheese) See recipe in this book.