Preparation Pur&eaacute;e tomatillos, half of tomatoes, and half of onion with chile, garlic, vinegar, and 1 1/4 teaspoons salt in a blender until smooth. Force through a medium-mesh sieve into a bowl, discarding solids. Stir in remaining tomatoes and onion, water, oil, and cilantro. Chill until cold, at least 1 hour and up to 4 hours.
Preparation Pur&eaacute;e tomatillos, half of tomatoes, and half of onion with chile, garlic, vinegar, and 1 1/4 teaspoons salt in a blender until smooth. Force through a medium-mesh sieve into a bowl, discarding solids. Stir in remaining tomatoes and onion, water, oil, and cilantro. Chill until cold, at least 1 hour and up to 4 hours.