1Heat a drizzle of oil in a small, heavy oven-proof pot set over medium-high heat. Season the ribs with salt and pepper and brown on all sides; add the balsamic vinegar and cook for a minute, scraping up the browned bits from the bottom of the pan.
3Pour the wine overtop, and add enough stock to come about halfway up the sides of the ribs. Cover and cook at 300F for 2 1/2-3 hours, until the meat is very tender. When cool enough to handle, pull the meat off the bones and set aside. Meanwhile, set a heavy skillet over medium-high heat; add a generous drizzle of oil and cook the onions for 10 minutes, until soft and golden. Add the balsamic vinegar (if you’re using it) and cook for a minute, until it evaporates; add the brown sugar, season with salt and pepper and cook for another 5-8 minutes, until deep golden. Set aside to cool.
5To assemble your grilled cheese sandwiches, slice the roasted garlic oval on a slight diagonal and layer with grated cheddar, caramelized onions, short rib and more cheddar. If you like, stir some grated Parmesan cheese into soft butter and spread on the outside of the sandwich; alternatively, brush with olive oil. Grill in a panini grill or in a hot skillet, turning as needed, until the cheese has melted and the sandwich is crusty and golden.