A slow simmer gives this tomatillo barbecue sauce its rich flavor. Serve over grilled chicken, fish, or shrimp.
Cook all ingredients in a large stockpot over medium-low heat 2 hours or until tomatoes and tomatillos are tender. Cool.
Process green tomato mixture, in batches, in a food processor or blender until smooth.
Note: Sauce may be stored in refrigerator up to 1 week.