- 4 tablespoons butter
- 3 Spanish (or yellow) onions, finely diced
- 2 rosemary sprigs
- 3 thyme sprigs
- 1 cup granulated sugar
- ¾ cup white balsamic vinegar
- ⅛ teaspoon salt
- Melt the butter in a large, heavy-bottomed pot or skillet over medium-low heat.
- Add the diced onions and begin to caramelize, stirring occasionally, until soft and lightly golden, about 20 minutes. The onions should be about halfway to caramelized by this point.
- Tie the rosemary and thyme together with kitchen twine and add to the onion mixture.
- Add the sugar and let dissolve into the onions without stirring, about 5 minutes.
- Increase the heat to medium-high and cook until darkened in color and thick, about 5-10 minutes. Avoid stirring unless the mixture starts to burn.
- Reduce the heat to low and add the white balsamic vinegar, stirring until thick, about 5-10 minutes.
- Remove from the heat, remove the herb bundle, and stir in the salt. Let the onion jam cool completely, then store or serve as desired.