In a food processor, combine the flour & salt. Pulse to sift them. Add the butter & pulse again until the mixture resembles coarse crumbs. Add the sugar & pulse several times.
In a small bowl, combine 4 tblsp of the water with vinegar. Sprinkle mixture on the flour. Pulse just until the dough forms large, moist clumps. It should not come together to form a ball. Add the remaining water, 1 tsp at a time, if necessary, to form moist clumps.
Turn the clumps out onto a lightly floured counter and knead them gently to form a dough. Flatten dough into a disk. Wrap in foil & refrigerate for 30 min.
On a floured board, roll the dough to a 13-in round. Lift it onto the rolling pin & ease into the tart pan. Alternatively, roll the dough to an 8-in round. Set it in the center of the pan & with the heel of your hand, press the dough into the bottom & sides. In either case, the dough should come up to the top edge of the pan. Press it firmly against the fluted sides. With a fork, prick the bottom of the pastry. Refrigerate.
Set the oven to 400º. Peel the apples, quarter & core them. Cut the quarters into thirds. Arrange the apples in concentric circles in the pastry. Set the pan on a rimmed baking sheet & transfer to the oven. Bake the tart for 30 min or until the pastry at the edges is lightly browned.
In a bowl, combine the eggs, extra yolk, & sugar. Whisk for 1 min. Whisk in the cream. Pour the custard over the apples - the custard should come only to the top of the pastry. Return the tart to the oven. Continue baking 15-20 min or until the custard is set. Remove from oven & cool slightly on a wire rack.
Sprinkle with confectioners sugar before serving.