In a large saucepan over medium-high heat, place 4 cups water, the guajillo chilies, garlic cloves and white onion and bring to a boil. Reduce the heat to simmer until the chiles are soft and tender, about 25 minutes. Transfer the boiled vegetables, the tomato and 2 cups of the boiling liquid to a large blender and set aside to cool before blending. Process until smooth. Season with 1 teaspoon salt and a pinch of black pepper.
In a medium, heavy saucepan, heat the vegetable oil over medium heat. Strain the pureed guajillo salsa into the pan. Add the bay leaf and simmer until thickened, about 10 minutes. Taste for seasoning, adding additional salt and pepper as desired.
Reserve for enchiladas and pork.
Cook's Note: For ease of preparation, you can use 2 store-bought, canned whole tomatoes, seeded, in place of 1 fresh, boiled tomato.