This is a very simple recipe. All it requires is time.
- Reduce a lot of sliced red onion over medium-low heat cooking with a neutral oil with a little bit of salt to draw out the moisture
- Stir regularly and make sure none burns (in the photo, each progression was roughly 20-30 minutes of time)
- After the onions are caramelized mix in balsamic vinegar, which is sweet because of its cooked grape must, and water until you have the sweetness and consistency you wish
- Pour into sterile jars while still hot and seal