Peel and dice (or slice) the onions.
In a large heavy-bottomed pot/skillet, add the oil and heat over medium-high heat.
Once hot, add the onions to the pan and cook for 15 minutes, stirring often, until the onions are tender and golden-brown.
Reduce the heat to low, add the thyme and bay leaf, and cook for 3-5 minutes.
Sprinkle the sugar over the onions, leaving it to cook for 5 minutes, untouched.
Increase the heat to high and cook for 5 minutes, or until the sugar caramelizes and turns golden-brown, without stirring.
Add the balsamic vinegar and stir, then simmer on low for 5 minutes.
Finally, remove the herbs from the pan, taste, and season the sweet onion jam.
Allow it to cool before transferring it to a sterile jar to store.
