" Start with at least 8 thinly sliced onions. Set your largest skillet, or a large Dutch oven, over medium-high heat. Add enough butter, olive oil, or some of each, to generously coat the bottom of the pan. Let the fat heat up until it shimmers, then add the onions and season lightly with salt. Though this will draw water out and delay browning initially, it will also soften the onions and lead to more even browning in the long run. Reduce the heat to medium, and keep an eye on the onions, stirring as necessary to keep from burning, or from browning too quickly in any one spot of the pan. It’ll take a while for them to cook all the way through—at least 45 minutes, and up to an hour. "

― Samin Nosrat , Salt, Fat, Acid, Heat: Mastering the Elements of Good Cooking