Preheat the oven to 350 degrees. Heat the oil in a medium heavy saucepan or skillet over medium low heat. Saute the rice, stirring constantly, until golden and crackling, about 5 minutes. Add the onions and Serranos and cook until the onions just soften. Then add the garlic and saute until the aroma is released. Pour in the stock or water and the tomato salsa, mixing well to combine. Transfer to a 4 quart baking dish or casserole. Cover with foil and bake until the liquid is absorbed and the rice is tender, 3040 minutes. Stir and serve hot.

Heat the vegetable oil in a medium skillet over moderate heat. Cook the onions until soft, about 10 minutes. Transfer to a food processor fitted with the metal blade, or a blender. Add the remaining ingredients except salt and puree, in batches if you are using a blender, until smooth. Pass through a medium strainer, pressing with a spatula or wooden spoon to push through as much pulp as possible. Pour into a saucepan, and add the salt. Bring to a boil, reduce to a simmer and cook, uncovered, 20 minutes. Adjust seasoning and serve as dipping sauce for chips or use in other recipes.