- For harissa sauce, toss onions with salt in a large bowl. Place salted onions in a strainer and drain overnight.
- Rehydrate arbol and pasilla chiles in simmering water until soft. Remove from water and pat dry.
- Mix all ingredients except for oil in a food processor. Once combined, slowly add oil in steady stream.
- For ribs, heat grill to about 325 degrees or medium-low heat.
- Season ribs with salt, pepper, and oil. Grill ribs over charcoal or hardwood until internal temperature reaches 155 degrees.
- Lightly brush harissa sauce on all sides of ribs. Turn off grill and let ribs sit for 20 minutes on grill, closed if there is a top.