To make the lemon tart:

1. Slice the lemons paper-thin, discarding the thicker stem end and any seeds. They will slice easier if you chill them before hand. Put them in a nonreactive bowl (stainless steel or glass) and, using a spoon or your hands, toss with the sugar. Cover and let sit at room temperature for at least 3 hours or for up to overnight. If any seeds are still left, they will usually float to the top, where they are easily fished out. If you are using the more tender-skinned Meyer lemons, you can proceed to the next step without letting them sit, as the skins don’t need sugar to tenderize them.
2. Use 1 pastry round (recipe below), rolled out to 1/8 inch thick, to line a 10-inch tart pan with a removable bottom, easing it into the bottom and sides leaving a 1-inch overhang. Set aside.
3. In a small bowl, whisk the eggs and salt together until blended. Add the eggs to the lemon mixture, mixing thoroughly. Pour the mixture into the pastry-lined tart pan. The mixture will be very liquid, so you must evenly distribute the lemon pieces in the pan.
4. To make the egg wash, in a small bowl, whisk together the egg yolk and cream. Brush the rim of the pastry with the egg wash to help the top pastry round adhere. Lay the second pastry round over the filling and trim the overhang for both rounds to 1/4 inch. Crimp the edges as you would for a pie, making sure you have a good seal. Brush the top of the pie with the egg wash and then sprinkle the sugar evenly over the top. Chill for about 30 minutes. While the pie is chilling, position a rack in the lower third of the oven and preheat the oven to 350F.
5. Line a baking sheet with aluminum foil or parchment paper. Cut a few decorative slits in the top of the pie for air vents, and place the tart pan on the lined baking sheet. Bake the pie until it is deep gold on top and the filling is bubbling (visible through the vents), about 40 minutes. If the top is coloring too quickly, place a piece of foil or parchment loosely over the top. Let the pie cool completely before slicing to allow the filling to set properly. Serve at room temperature or slightly warmed with lightly whipped unsweetened cream (though the pie needs to cool completely for the filling to set up, it can be warmed up a little in the oven before serving). The pie will keep in the refrigerator for up to 4 days.

To make the tart dough:

1. In a small bowl, mix together salt and water. Keep very cold until ready to use.
2. Place flour and butter in the bowl of a food processor. Pulse briefly until mixture forms large crumbs. Add the salt water mixture and continue pulsing until the dough has just formed but is not smooth. You can also do this step manually using a pastry cutter or two knives.
3. On a lightly floured work surface, evenly divide dough. Form each piece of dough into a disk about 1 inch thick. Wrap each disk with plastic wrap and chill at least 2 hours and up to overnight.