pickled onions recipe

Ingredients: 1 large red onion, thinly sliced 1 cup white vinegar 1/2 cup water 1 tablespoon granulated sugar 1 1/2 teaspoons kosher salt Optional: 1/2 teaspoon black peppercorns, 1/2 teaspoon mustard seeds, 1/2 teaspoon coriander seeds, and a few sprigs of fresh herbs (such as thyme or dill)