Prepare the Onions – Use a sharp knife to trim ½-inch from the stem end and ¼-inch off the root end. Cut in half lengthwise with the stem-side down, then peel. Slice each half from root to stem into ¼-inch thick pieces.
Melt the Butter – Set a large, wide pan with high sides or a Dutch oven over medium-low heat. Add the butter, olive oil, and salt, and quickly stir to combine. Do not let the butter brown.
Soften the Onions – Immediately add in the onions and stir to coat. Increase the heat to medium. Using a wooden spoon, frequently stir until they begin to soften, 5 minutes. Reduce the heat to medium-low.Spread the onions into an even layer. After a few minutes, stir and scrape any browned areas on the bottom of the pan. Repeat this process every few minutes, for 10 minutes. Adjust the heat down if needed to prevent burning.
Deglaze and Caramelize – Make a well in the center of the pan. Add 2 tablespoons of water and scrape to dissolve any browned bits (fond) on the bottom. Spread the onions in an even layer. Stir and scrape every few minutes. As more brown fond forms, add 2 tablespoons of water every 5 minutes.Repeat the deglazing, stirring, and spreading process until soft and caramelized. Add as much water as needed to deglaze and cook. About 35 minutes for blonde, 45 minutes for golden brown, and 55 minutes for deep brown onions.
Recipe Yield: About 1 cup
Serving Size: About 2 tablespoons
Onion Selection: Yellow, sweet onions, red onions, or shallots can be caramelized. Use a mixture for more depth of flavor.
Cutting: Onions sliced lengthwise will hold their shape better and have a milder taste. Sliced crosswise, it will be a softer texture and more pungent taste (often used for French onion soup).
Water Substitute: Unsalted vegetable or chicken stock or broth can be added for a savory flavor. Wines like white or red can be used for a fermented taste with light acidity.
Storing: Cool completely and store in an airtight container for up to 7 days. Freeze in a resealable plastic bag for up to 6 months. Defrost before using.