I make this tart in a rectangular tart pan with removable bottom. It makes for a beautiful presentation. The tart can be served as a luncheon dish with salad, or can be cut into small squares as an hors d'oeuvres. —lisa volpe hachey
9-12 as a meal, or 24 pieces as an hors d'oeuvres
Place the flour and salt in the bowl of a food processor fitted with a metal blade. Add the bits of cold butter and PULSE the machine 8 times. Remove the cover, add the ice water 1 tablespoon at a time, pulsing the machine between additions until the dough forms large clumps. DO NOT allow the dough to form a ball around the blade.
Turn the dough out onto a flat surface and form into a large round (if using a round tart pan) or rectangular (if using a rectangular tart pan) mass. Place dough between two pieces of plastic wrap and, using a rolling pin, flatten the dough into the desired shape, rolling to about 1/2 inch. Chill dough for 1 hour or longer.
After dough has chilled, remove plastic wrap and place it on a flat surface that has been DUSTED with flour. Roll out the dough, turning it constantly so you know it isn't sticking to the table, until it is about an inch wider than the tart pan. Fold the dough in half ad carefully lift it onto the tart pan. Press the bottom ad sides of the dough into the pan, and run a rolling pin over the top of the pan to remove the excess dough.
Preheat oven to 375 degrees. Line the pastry with aluminum foil or parchment paper and fill with rice to weigh it down. Bake in preheated oven for 10 minutes, or until it begins to dry out. Remove foil and weights, prick bottom of pastry with fork, return to oven for 5 minutes more. Proceed with filling.
For the filling: Melt butter in a large skillet. Add sliced onions and cook over medium heat for 5 minutes, until onions are soft. Stir in the flour and cook 1 minute. Stir in the milk (half & half), bring to boil, reduce heat, and simmer for 3 minutes. Remove pan from heat. Beat in the cheese, eggs, and seasonings.
Spoon mixture into partially baked tart shell and bake for 25 minutes, or until golden brown and set. If during this final 25 minutes the edges become too brown, cover with foil. Cool slightly and unmold.