In a medium pot, add the guajillo, ancho, and árbol chiles and enough water to cover them completely. Bring to a boil over high heat. Remove the pot from the heat, cover, and let the chiles soak for 10 minutes to soften.
Using a slotted spoon, transfer the softened chiles to a blender. Add 1 cup of the chile-soaked water, ¼ cup of fresh water, and the tomato, crushed tomatoes, garlic, salt, and Mexican chocolate. Blend until completely smooth. This step may take a few minutes, depending on the power of your blender. Add more water if the sauce is too thick for your liking.
Heat the olive oil in a medium skillet over medium-high heat. Add the sauce and bring to a simmer. Reduce the heat to low and simmer for 3 minutes.
Cover and store until ready to use. It’s perfect for making chicken enchiladas, red chilaquiles, and chicken enchilada soup.
