- 2 tablespoons olive oil
- 2 tablespoons unsalted butter
- 4 cups thinly sliced red onion
- 1/2 cup apple cider
- 1/2 cup cider vinegar
- 1/4 cup sugar
- 1 sprig fresh rosemary
- 1/4 teaspoon sea salt
- 1/4 teaspoon freshly ground black pepper
- Heat the olive oil and butter in a medium heavy-bottomed nonreactive saucepan over medium heat. When it is hot, add the onion and cook for about 15 minutes, stirring as needed, until it is caramelized.
- Add the apple cider, vinegar, sugar, rosemary sprig, salt, and pepper. Reduce the heat to medium-low and cook for another 30 to 35 minutes, stirring occasionally, until the onion has reached a jam-like consistency.
- Discard the rosemary sprig and set the jam aside to cool before using, or cover and refrigerate for up to 1 week.