Individual Potato-and-Onion Tartes Tatin

Ingredients in this Recipe

1 (17 1/4 ounce) standard package store bought puff pastry
1/4 cup balsamic vinegar
4 medium yellow onions, peeled, cut into 1/4 inch thick rounds
4 tablespoons (1/2 stick) unsalted butter, cold, cut into small pieces, plus more for pans
5 small new potatoes, peeled
All purpose flour, for dusting
Coarse salt and freshly ground pepper
Pinch of sugar

See Full Recipe at Martha Stewart