Serves: Makes 1 quart
Split, stem, and seed the chillies. Toast the chillies in a dry skillet over medium-high heat, turning and flattening with a spatula, until fragrant, about 3 minutes. Put the chillies in a heatproof bowl, cover with very hot water, and set aside until soft, about 30 minutes. Drain, reserve soaking liquid, chop chillies roughly, and set aside.
While the chiles soak, char the onion and garlic in the same dry skillet over medium heat until the onion blackens slightly and garlic softens in the skin, about 8 minutes. Cool, squeeze the garlic out of the skin, and put in a blender with chillies and onion. Puree to a paste, adding soaking liquid as needed (about 3/4 cup) to help the mixture break down.
Heat the oil in the skillet over medium-high heat. Add the chilli mixture and cook, stirring, until thick and fragrant, about 4 minutes. Add the tomato puree, coffee, sugar, 1 tablespoon salt, oregano, cloves, and cumin. Adjust the heat to maintain a gentle simmer and cook, stirring occasionally, until slightly thickened, about 15 minutes.
Stir in vinegar and season with salt to taste.
Cook's Note: For this recipe, we prefer Mexican oregano. It's stronger than Italian oregano, so it can hold its own with the other assertive flavors in this sauce.