The hardest thing about caramelized onions is being patient and letting them do their thing. To a sauté pan oven low heat add the butter, oil, onions and sugar. Toss to coat then let it cook. Every once in a while give it a little stir but otherwise, leave it. It takes about 45 minutes on the lowest low to reach the point of caramelization, the color of the onions will not be browned as if sautéed instead they will be have deepened in color and are incredibly tender.
While those fabulous onions are working you can get the rest of the panini ready. Cut the roll open and hollow putt the top part of the roll, it makes it a little easier to get all the goodness to stay put. Spread 2 Tbsp of the Brie spread on the bottom of each roll.
Put half the turkey on each roll... maybe a couple slices for snacking if you're like me. Then layer on the sliced apple (if you cut the apple in advance it will start to oxidize so wait until the onions are just about ready).
Now to finish off, pile on those AMAZING caramelized onions you have so patiently waited for. You certainly don't have to use all the onions, I saved a little bit to throw over a piece of grilled chicken for tomorrows lunch. Melt some cheddar over top and YUM! Back to the panini, now that everything is assembled place on a panini press on medium high heat and allow the weight to slowly press it down and give the bread a good crisp on it. I have the Cuisinart Griddler Panini and Sandwich Press and love it!