Ingredients
2 tablespoons olive oil
3 medium red onions (about 1 1/2 pounds), halved lengthwise and thinly sliced
coarse salt and ground pepper
1/2 cup red-wine vinegar
1/4 cup sugar
Preparation
In a large saucepan with a lid, heat oil over medium. Add onions, season with salt and pepper, and toss to coat. Cover and cook, stirring occasionally, until onions are very soft, 20 to 25 minutes.
Add vinegar and sugar; simmer over medium-low heat, uncovered, stirring occasionally, until syrupy and jam-like, about 30 minutes. Let cool.
