Caramelized onion jam is a test-kitchen favorite—it pairs well with numerous dishes and its savory sweetness and rich color belie its simplicity. The key to keeping it truly simple is moving the bulk of the time spent caramelizing the onions to the oven. With 4 pounds of onions in the pot, this saved us from a lot of stirring. Returning it to the stovetop, we added sugar, port, and vinegar and turned our onions into jam, ready for topping burgers, stirring into onion dip, accompanying cheese platters, or garnishing pizzas. For just the right consistency, make sure you let the jam come to room temperature before using.
Using yellow onions is key; sweet onions, such as Vidalia or Walla Walla, will turn gummy. Slicing the onions “pole to pole,” or from the root to the stem, gave us better results than slicing them crosswise along the equator, which, once cooked, produced unappealing stringy pieces.
We cook the onions covered for the first hour to keep them moist. Then we crack the lid to let excess moisture evaporate and encourage browning. Once browning begins, it’s key to stir the onions every half hour.
Once the onions have caramelized, pull them from the oven, dump the whole mess onto a cutting board and chop into 1-inch pieces, then transfer them to a large saucepan.
When we first made this recipe, we used a simple combination of port and sugar to build the jammy base, but the finished product was a clumpy mess and too sweet. In the end, we found that adding water loosens the mixture, white wine vinegar balances the sugar, and a sprinkling of fresh thyme adds depth.
You’ll know the jam is finished when it turns thick and glossy and a spatula or wooden spoon leaves a trail when dragged across the bottom of the saucepan. Transfer jam to jar with tight-fitting lid, let cool to room temperature, then cover and refrigerate.
Find this and other great DIY recipes in The America’s Test Kitchen DIY Cookbook.