Instructions

• Heat a large cast‑iron or heavy‑bottomed skillet over medium‑high heat. Add 2 tablespoons butter and 1 tablespoon canola oil and melt until the butter is foaming.
• Add 3 large yellow onions (peeled, halved, and thinly sliced), 1 teaspoon kosher salt, and the leaves from 3 sprigs fresh thyme. Toss to coat and cook for about 5 minutes, stirring frequently, until the onions begin to soften and turn translucent but are not browned.
• Reduce the heat to medium‑low and cover the skillet with a lid. Continue to cook, stirring and scraping the bottom of the pan every 10–15 minutes so the onions cook evenly.
• If the onions begin to stick or look like they are burning, add a splash of water and stir to deglaze the pan, then continue cooking.
• During the last 10 minutes of cooking, remove the lid and add 1 tablespoon white balsamic vinegar, if using. Cook uncovered, stirring occasionally, until the onions are deep golden brown and jammy. Total cooking time will be up to about 1 hour from the start, depending on your stovetop and pan.
• Remove from heat and serve immediately, or cool and store in an airtight container in the refrigerator for up to one week.