If you were to plot condiments on a family tree, you’d find that these pickled red onions are the wild-child grand-daughter of caramelized onion jam and the second cousin of the hot dog relish you find at the ball park. They are sophisticated, a little bit slippery, and equally at home draped across a hamburger or dolloped on a salad of baby arugula.
Prepare a boiling water bath and 3 regular-mouth pint jars. Place the lids in a small saucepan, cover them with water, and simmer over very low heat.
Combine the vinegar, 1-1⁄2 cups water, sugar and salt in a pot over high heat and bring the brine to a boil.
Add sliced onions to brine and stir to combine. Reduce heat to medium and simmer briefly to soften onions.
Meanwhile, combine the remaining spices in a small bowl and stir to blend. Add the spice blend to the sterilized jars, distributing evenly.
Using tongs, evenly divide the onions between the 3 jars. Pour hot brine into each jar, leaving 1⁄2 inch headspace. Gently tap the jars on a towel-lined countertop to help loosen any bubbles before using a wooden chopstick to dislodge any remaining bubbles. Check the headspace again and add more brine if necessary.
Wipe the rims, apply the lids and rings, and process in a hot water bath for 10 minutes.
Let these pickles cure for at least 48 hours before eating.