- 6 tablespoons unsalted butter
- 15 medium yellow onions (about 6 pounds total), halved lengthwise and sliced 1/4 inch thick
- 2 teaspoons coarse salt or 1 teaspoon table salt
- 1 tablespoon sugar
In an 8-quart Dutch oven or heavy pot, melt butter over medium-high. Add onions and salt. Cook, stirring often, until softened and just beginning to brown, 35 minutes.
Reduce heat to medium. Add sugar and cook, stirring often to scrape up any browned bits stuck to bottom of pot, 35 to 40 minutes (lower heat if bottom of pot begins to scorch).
When done, onions should be deep golden brown and have a jam-like consistency. Remove from heat; season with salt. Let cool completely.