1. Caramelized onion pizza - we weren't gonna be home for dinner so that was out
2. Caramelized onion "jam"(just as a topping for bread) - not very practical
3. French onion soup - maybe if it wasn't 98 degrees out
4. Caramelized onion tart! YES!
To make caramelized onions the best, you need about 20 minutes to a half hour, and some patience. I used about 4-5 medium sized onions, sliced thinly in semicircles. Add some olive oil in a large saute pan over medium high heat (use a pan with large surface area so the onions saute the best). Normally when quick sauteeing onions, you'd wait until the oil is heated through before adding the onions, but you don't want to burn these onions, they cook low and slow basically. So add the onions as soon as you add the oil & stir to coat. Season with salt & pepper and saute until softened for a few minutes. Add 2 heaping tablespoons of brown sugar, and 2 tbsp. balsamic vinegar and stir. The brown sugar intensifies the sweetness of the onions as they cook. Stir well for a few minutes on high heat and then lower the heat to medium. Let saute for 15 minutes, or until golden brown and very soft, stirring well every few minutes, making sure the onions aren't burning.
Preheat the onion to 425 degrees. In the meantime, unfold a thawed sheet of puff pastry on a floured surface, and roll out all the sides to a large square and place on a baking sheet. Whisk 1 egg and brush on the whole pastry, leaving a 1/2-1" border. Brushing the egg wash all over helps seal the pastry in the oven so that it doesn't get soggy from the topping. Let the onions cool a bit before adding them to the pastry. The onions shrink down from a ton to about a cup or 2! Add all the onions to the pastry, leaving about 1/2"-1" border all around. Fold over all the sides and crimp with a fork, then brush the new exposed borders. Bake for 20 minutes until pastry is golden. Garnish with fresh parsley.
Hope you enjoy your puff as much as I do!