Servings: Makes 5 cups
Toast the coriander seed in a small, dry sauté pan over medium heat until its aroma is released, about 2 minutes. Add the mustard seed to the same pan and toast for 1 additional minute. Soak the onions in ice water, then drain and pat dry.
In a small sauce pot, slowly bring the vinegars, sugar, bay leaves and thyme to a boil. Adjust the flavor with water if too acidic. Pour this mixture over the onions in a medium, heat-proof bowl: allow to sit for 5 minutes. Drain off the excess vinegar, season with salt and pepper, then toss lightly with the olive oil. Store the picked onions in an airtight jar in the refrigerator until ready for use.