Melt in a large nonstick skillet over medium-high heat:
Add and cook, stirring, for 5 minutes, or until softened:
Stir in:
Cook, stirring, until the onions turn golden brown and are very soft. Add:
Boil, stirring occasionally, until almost all the broth has evaporated, about 15 minutes; watch carefully so that it doesn’t burn. Transfer to a bowl and stir in:
Let cool completely, then stir in:
Chill for 1 hour before serving.