How to Make It
Bring a pot of water to a boil. Boil the onions over high heat for 4 minutes. Drain and let cool. When the onions are cool enough to handle, slip off their skins.
Pack the onions into four 1/2-pint jars. Add 2 cloves, 1/4 teaspoon of mustard seeds and 2 strips of lemon zest to each jar.
In a small saucepan, combine the water, vinegar, sugar and salt and bring to a boil, stirring to dissolve the sugar. Pour the brine over the onions to cover. Let cool, then seal the jars and refrigerate the onions for at least 3 weeks.