In a large saucepan, over medium high heat, heat the butter and sweat the onion and garlic until translucent. Add the tomatoes and simmer for 15 minutes. Add the next 8 ingredients and continue cooking for 20 minutes. Puree the mixture in a food processor, pour into a bowl and whisk in the peanut butter, soy sauce, vinegar and chipotle. Preheat grill.

Remove ribs from marinade. Grill the ribs turning and brushing with the sauce until cooked through.