Yes - it's one of the yummy toppings I ordered recently at a fantastic hamburger place called The Counter. We recreated our own gourmet toppings The Counter experience recently for a family gathering. I just had to have their onion marmalade.
I searched online, combined a few recipes and came up with this:
3 sliced onions 1/3 cup red wine 1/3 cup red wine vinegar (I had to substitute white) 1/4 cup brown sugar 1/4 cup honey
Combine and simmer for 30 minutes until liquid is absorbed.
I also made a herbed goat cheese topping by putting soft goat cheese, fresh chives and basil, plus garlic in the good processor.
(sorry - the picture above was borrowed temporarily. I forgot to take one. I'll change it next time I make this yummy recipe)