Step 1

Thinly slice the onion with a knife or mandoline, then place in a 16-ounce jar. Add any optional flavor boosters.

Step 2

In a measuring cup, stir together the water, vinegar, honey, and salt.

Step 3

Carefully pour the brine into the jar over the onions. Cover with a lid and refrigerate. They'll be ready to eat after about an hour in the fridge (they'll be vibrant pink), and will keep for 2 to 3 weeks in the fridge.