3 lbs. round red potatoes, cut in 1-inch pieces
1 small red onion, cut in wedges (1/2 cup)
6 cloves garlic, minced
2 Tbsp. olive oil
1 cup frozen whole kernel corn
3/4 cup mayonnaise
2 Tbsp. cider vinegar
1 1-oz. envelope dry ranch salad dressing mix
1/4 tsp. cayenne pepper (optional)
1 stalk celery, bias-sliced
3 hard-cooked eggs, peeled and chopped
1 avocado, halved, seeded, peeled, and chopped (optional)
Salt and ground black pepper
Fresh Italian (flat-leaf) parsley, coarsely snipped (optional)