Bring a kettle of water to a boil. Add the dried chiles to a large mixing bowl and cover them with hot water. Allow chiles to soak 2 to 3 minutes, until re-hydrated. Strain the water and remove the stems and seeds from the chiles. Set aside. Note: For a spicier sauce, save some of the seeds so that you may add them to the sauce.

In a large skillet, heat the oil to medium. Add the onions and saute, stirring occasionally until translucent, about 10 to 12 minutes.

Add the tomatillos and garlic and saute another 5 minutes.

Add the re-hydrated chiles, diced tomatoes, tomato paste, broth, and chocolate. Bring mixture to a full boil, then reduce the heat to a simmer. Cover the skillet and allow mixture to cook 45 minutes to 1 hour.

Add the contents from the skillet to a blender and blend until completely smooth. Be sure to keep the lid of the blender slightly cracked to allow steam to escape.

Taste the sauce for flavor and add sea salt to taste.

If you aren’t using the sauce immediately for a recipe, store it in a large seal-able glass jar in the refrigerator for up to 3 weeks. You can also freeze the sauce.