Pour water to a depth of about 2 inches into a saucepan, place over medium heat, and bring to a simmer. Combine the lemon juice, whole eggs, yolk, sugar, and salt in a stainless steel bowl that will rest securely in the rim of a saucepan over, not touching, the water. (Never let the egg yolks and sugar sit together for more than a moment without stirring; the sugar will cook the yolks and turn them granular.)

Place the bowl over the saucepan and continue to whisk until the mixture becomes very thick and registers 180° F on a thermometer. This will take 10 to 12 minutes. If you don't have or trust your thermometer, don't worry. It should thicken to the point that your whisk leaves a trail through the curd.

Remove the bowl from over the water and let cool to 140° F, stirring from time to time to release the heat.

Meanwhile, cut butter into 1-tablespoon (15-ml) pieces. When the cream is ready, leave it in the bowl if using an immersion blender, or pour it into a countertop blender. With the blender running, add the butter 1 tablespoon at a time, blending after each addition until incorporated before adding the next piece. The cream will be pale yellow and opaque and quite thick.

You can use the cream immediately, or pour it into a storage container with a tight-fitting lid and refrigerate for up to 5 days.

To use after refrigeration, if necessary, gently heat in a stainless steel bowl set over simmering water until it has softened, whisking constantly.

Using a stand mixer fitted with the paddle attachment, combine the butter, sugar, and salt and mix on medium speed until smooth. Mix in 1 egg. Add the remaining egg and mix until smooth. Stop the mixer and scrape down the sides of the bowl with a rubber spatula. Add the flour all at once and mix on low speed just until incorporated.

On a lightly floured work surface, divide the dough into 4 equal balls and shape each ball into a disk 1/2 inch thick. Wrap well in plastic wrap and chill for at least 2 hours or overnight.

Preheat the oven to 325°F. Dock (make small holes in) the bottom of the tart shell with a fork or the tip of a knife, making tiny holes 2 inches apart. Place in the oven and bake for 7 to 10 minutes for a partially baked large shell. The pastry should be lightly colored and look dry and opaque. Check the shell(s) during baking and rotate the pans if necessary for even color. If you want to brush the shell(s) with a glaze (see headnote), beat the egg with the salt in a small bowl. A minute or two before the desired color is reached, remove the shell(s) from the oven and lightly brush the bottom and sides with the glaze. Return the shell(s) to the oven and bake until the desired color is reached and the glaze is set.

For a fully baked shell, proceed as directed for a partially baked shell, but bake until golden brown, about 5 minutes longer.

Let cool completely on wire racks. The pastry shells will keep, well wrapped, in the refrigerator for up to 1 week or in the freezer for up to 2 weeks.

Any leftover dough can be used as a simple cookie dough. This dough keeps exceptionally well, so make some for use now and freeze the rest for future use (it will keep for up to 3 weeks), either in disks or in rolled-out rounds. If you roll out all the rounds to freeze for future use, place a sheet of parchment or waxed paper between them to prevent them from sticking to one another when you thaw them.

This recipe can be easily halved.