pickled red onions recipe

**Ingredients:** - 1 large red onion, thinly sliced - 1 cup apple cider vinegar (or white vinegar) - 1 cup water - 1 tablespoon granulated sugar - 1 1/2 teaspoons salt - Optional flavorings: 1 garlic clove, smashed; 1 teaspoon whole black peppercorns; 1/2 teaspoon red pepper flakes; 1 bay leaf