I can’t find an online version of this recipe, but it was good enough to earn a 5 mushroom ratings so I’ll give it to you here.
FOR PICKLED ONION
1 red onion (6 ounces), sliced crosswise 1/4 inch thick
1/2 cup cider vinegar
3/4 cup water
1/2 teaspoon salt
FOR CHIPOTLE MAYONNAISE
1 1/2 teaspoons chopped canned chipotle chiles in [...]