The crust is almost a big shortbread cookie, not the easiest to work with, but worth the bother. If it tears when you roll it out, don't despair. Do the best you can to line your tart pan and piece together bits where necessary.
Place the flour, salt, and 1/2 cup of the sugar in a mixer bowl. Add the chilled butter and mix at medium speed until the mixture resembles grainy meal. Add the ice water and 1 of the egg yolks and mix just until a mass begins to form. Remove from the bowl, roll into a disk, wrap in plastic wrap, and chill in the refrigerator for 45 minutes.
Meanwhile, in a medium bowl, beat together the remaining 2 yolks with the eggs. Beat in the remaining 1/2 cup sugar, the lemon juice, and the crème frâiche. Stir in the tablespoon of melted butter. Set the mixture aside.
Preheat the oven to 375 °F (180 °C).
Flour a work surface and roll the pastry into a 10" circle. Line a 9" tart ring with the pastry. Prick the bottom of the pastry in a few places with a fork and place in the freezer for 5 minutes.
When the dough is well chilled, line it with aluminum foil, making sure to work the foil into the corners. Place the piecrust in the freezer to chill for 5 minutes, then transfer to the bottom rack of the oven and bake for 10 minutes. Be certain that the pastry is well chilled before you bake it.
Remove the tart pan from the oven and remove the foil. Place the tart shell on the middle rack of the oven and pour in the lemon mixture. Bake until the lemon mixture is set, about 20 to 25 minutes.
Remove the tart from the oven and cool completely before unmolding. (This can be made a day in advance and kept tightly wrapped at room temperature; do not refrigerate).