I could eat this stuff by the spoonful!!  It is good on beef, pork, chicken.  Use it as a sandwich spread.  Great on hamburgers.  

Ingredients:

• 1 Tab Olive oil
• 4 medium onions, thinly sliced (about 8 cups)
• Kosher salt and freshly ground black pepper
• 2/3 c balsamic vinegar

Instructions:

1. Heat the oil in a large skillet over medium heat until it slides easily across the pan.
2. Add the onions, salt, and pepper and cook, stirring occasionally, for about 20 minutes, until the onions are soft.
3. Reduce the heat to medium-low.
4. Cook, stirring frequently, for about 10 minutes, until the onions appear dry.
5. Add the vinegar.
6. Reduce the heat to low.
7. Continue cooking, stirring occasionally, for about 1 hour, until the onions are soft and dry.
8. Serve warm or at room temperature.
9. Store the marmalade in the refrigerator. It will keep for several weeks.

Serves:  2 to 3 cups

Source: A variation on several recipes.  Some add sugar, it’s up to you how sweet you like your savorys.