When it comes to caramelized onions, the pan you cook them in plays a crucial role. A well-seasoned, slick cast iron skillet works best to achieve a soft, sweetened pile of onions.

The well-sized cast iron skillet can handle piles of onions, cook them evenly with uniform heat distribution, and allow for a layer of fond to stick to it, which is important.

Fond refers to the jammy, sticky, browned bits that become glazed onto the pan’s bottom. Scraping it and working it into the onions as they cook yields an extra caramelized flavor.

Unlike cast iron skillets, non-stick skillets don't allow fond to develop and stick to their surfaces. Plus, vigorous scraping isn't something you can do with a Teflon-coated pan.