1 small Red onion; peeled, sliced 1/8 inch
1/4 teaspoon Black peppercorns
1/4 teaspoon Cumin seeds
1/2 teaspoon Dried oregano, preferably Mexican
2 Garlic cloves; peeled, halved
1/4 teaspoon Salt
1/3 cup Cider vinegar
Blanch the onion slices in boiling salted water for 45 seconds, then drain and place in a medium-sized bowl. Coarse grind the peppercorns and cumin in a mortar or spice grinder, and add to the onions. Add the remaining
ingredients plus enough water to barely cover. Stir well and let stand for several hours until the onions turn bright pink.
Covered and refrigerated, the onions last several weeks.
Source: Rick Bayless