Step 1

Slice the onions. Trim the tip and root from 2 to 4 yellow onions. Halve each onion from root to stem, then remove the skins. Thinly slice each half from root to stem.

Step 2

Heat the fat. Melt 2 tablespoons unsalted butter in a large skillet over medium heat, or heat 2 tablespoons olive oil until shimmering.

Step 3

Add the onions. Add all the onions to the skillet and stir them gently to coat with the fat.

Step 4

Caramelize the onions. Cook the onions, checking on them every 5 minutes. Stir the onions and scrape up any fond that forms on the bottom of the skillet with a wooden spoon. Exact cooking times will vary with the number of onions you're cooking, their liquid and sugar content, and their age.• Around 10 Minutes: Onions will start to soften and turn translucent in spots. They will release a lot of liquid into the pan.• Around 20 Minutes: Onions will be very soft and starting to break down. Some onions will start to show spots of caramelization and you may see some fond starting to build up in the pan. They will also start to smell caramelized. Adjust the heat if the onions seem to be cooking too quickly or you notice any burnt spots.• Around 30 Minutes: Onions should be light blonde in color and starting to become jammy. More fond is starting to build up, but it should still be fairly easy to scrape it up with the evaporating liquid from the onions.• Around 40 Minutes: Onions are golden and starting to smell very caramelized. Taste one — if you like the way they taste, you can stop now! For even deeper caramelized flavor, continue cooking.

Step 5

Deglaze the pan and salt the onions. When your onions have finished cooking, pour in 1/4 cup wine, broth, balsamic vinegar, or water. As the liquid bubbles, scrape up the fond and stir it into the onions. Use additional liquid as necessary to scrape up all the fond. Season with 1/2 teaspoon kosher salt.

Step 6

Add baking soda, if desired. Mix 1/8 teaspoon baking soda into 1 tablespoon water until dissolved, then add to the onions. Cook, stirring constantly, until the water evaporates, about 30 seconds.