Sauté onions in oil over medium heat.
Add balsamic vinegar and sprinkle sugar over onions.
Continue to cook to caramelized onions for about 10-15 minutes.
Remove from heat. Set aside.
Grill Beef Franks for about three to five minutes.
Sandwich in baguettes then top with caramelized onions, mustard and some flat leaf parsley.
Serve while hot.
Happy cooking, Foodies!