This is great on burgers or paninis, especially ham and cheese. Also use on top of grilled chicken. It looks best with the onion cut lengthwise into 1/4 inch wedges, rather than rings. It will keep in fridge for up to 2 weeks.
Heat olive oil in a skillet over medium heat. Add the onions and cook for 5-8 minutes, until tender and translucent. Add the sugar and cook, stirring occasionally, for 15-20 minutes, until golden brown.
Add remaining ingredients and cook, stirring often to avoid scorching, for 20 minutes, or until thick and jamlike. The slower it is cooked, the richer the jam will be.
Store tightly covered in refrigerator for up to 2 weeks.