Caramelized Onion Tartlets without crumbs

1 (8 ounce) can refrigerated crescent dinner rolls 1 tablespoon olive oil 1 large sweet onion , thinly sliced (about 3 cups) 2 teaspoons fresh thyme , chopped[...]

2 teaspoons olive oil 2 small red onions , thinly sliced 2 small yellow onions , thinly sliced 1 tablespoon white balsamic vinegar 1 sheet frozen puff pastry[...]