3 medium Yukon gold potatoes (3/4 pound total), peeled and cut into 1/2-inch
Extra-virgin olive oil, for brushing
1 large egg beaten with 1 tablespoon milk
Coarse sea salt
Preheat the oven to 400°. On a lightly floured work surface, roll out the puff pastry 1/8 inch thick. Using a sharp knife, cut out an 11-inch round. Fold the round in half and transfer it to a 10-inch springform pan 2 inches high. Unfold and gently pat the pastry up the sides of the pan. Refrigerate the pastry until well chilled, about 10 minutes.
Arrange the potato wedges in overlapping circles on the bottom of the tart. Tuck any extra potato wedges in the center. Lightly brush the potatoes with olive oil and fold the pastry rim over them. Brush the egg wash on the pastry rim. Bake the tart for about 1 hour, or until the pastry is deeply browned and the potatoes are tender. Sprinkle the potatoes with salt and let the tart cool on a rack for about 5 minutes. Unmold the tart, cut it into wedges and serve.