In a medium bowl, combine onion, the ice water, and vinegar. Let stand for 30 minutes. Meanwhile, remove and discard the thin brown papery husks from the tomatillos. Rinse tomatillos and finely chop (you should have about 3/4 cup).Advertisement
Drain onion; stir in tomatillos, cherry tomatoes, plum tomatoes, cilantro, chile pepper, and lime juice. Season to taste with salt and black pepper. Cover and chill for at least 1 hour or up to 24 hours.
Tote in an insulated cooler with ice packs. Serve with baked tortilla chips.
Tip: Because chile peppers contain volatile oils that can burn your skin and eyes, avoid direct contact with them as much as possible. When working with chile peppers, wear plastic or rubber gloves. If your bare hands do touch the peppers, wash your hands and nails well with soap and warm water.