Once the lemon curd ingredients have been combined, cook the curd immediately or it will have a grainy texture. The shell should still be warm when the filling is added. If the shell has cooled, place it in the oven just before you start the curd and heat it until warm, about 5 minutes. Instead of dusting it with confectioners’ sugar, you can serve the tart with whipped cream.

TART DOUGH
1 large egg
1 tablespoon heavy cream
1/2 teaspoon vanilla extract
1 1/4 cup (6 1/4 ounces) all-purpose flour
2/3 cup (2 2/3 ounces) confectioners’ sugar,
— plus extra for dusting
1/4 teaspoon salt
8 tablespoons unsalted butter,
— cut into 1/4-inch pieces and chilled

LEMON CURD
2 large eggs plus 7 large yolks
1 cup (7 ounces) granulated sugar
1/4 cup grated lemon zest plus 2/3 cup juice,
— approximately 4 lemons
Pinch salt
4 tablespoons unsalted butter,
— cut into 4 pieces
3 tablespoons heavy cream

FOR THE TART DOUGH:

1. Whisk egg yolk, cream, and vanilla together in bowl. Process flour, sugar, and salt in food processor until combined, about 5 seconds. Scatter butter over flour mixture; pulse until mixture resembles coarse cornmeal, about 15 pulses. With processor running, slowly add egg yolk mixture and process until dough just comes together, about 12 seconds.
2. Turn dough onto sheet of plastic wrap. Form dough into 6-inch disk, wrap tightly in plastic, and refrigerate for 1 hour. Let chilled dough sit on counter to soften slightly, about 10 minutes, before rolling.
3. Roll dough into 11-inch circle on lightly floured counter. (If dough becomes too soft and sticky to work with, slip it onto baking sheet and refrigerate until workable.) Place dough round on baking sheet, cover with plastic, and refrigerate for about 30 minutes.
4. Remove dough from refrigerator, but keep dough on sheet. Loosely roll dough around rolling pin and gently unroll it onto 9-inch tart pan with removable bottom, letting excess dough hang over edge. Ease dough into pan by gently lifting edge of dough with your hand while pressing into corners with your other hand.
5. Press dough into fluted sides of pan, forming distinct seam around pan’s circumference. (Finished edge should be 1/4 inch thick. If some sections of edge are too thin, reinforce them by folding excess dough back on itself.) Run rolling pin over top of tart pan to remove any excess dough. Wrap dough-lined pan loosely in plastic, place on large plate, and freeze until dough is firm, about 30 minutes, before using.
6. Adjust oven rack to middle position and heat oven to 375 degrees. Set dough-lined pan on rimmed baking sheet. Spray 1 side of double layer of aluminum foil with vegetable oil spray. Press foil, sprayed side down, into pan, covering edges to prevent burning; fill with pie weights. Bake until tart shell is golden brown and set, about 30 minutes, rotating pan halfway through baking. Transfer sheet to wire rack and carefully remove foil and weights. (Shell must still be warm when filling is added.) Do not turn off oven.

FOR THE LEMON CURD:

Whisk eggs and yolks together in medium saucepan. Whisk in sugar until combined, then whisk in lemon zest and juice and salt. Add butter and cook over medium-low heat, stirring constantly, until mixture thickens slightly and registers 170 degrees, about 5 minutes. Immediately pour mixture through fine-mesh strainer set over bowl and stir in cream.

Pour warm lemon curd into warm tart shell. Bake tart on baking sheet until filling is shiny and opaque and center jiggles slightly when shaken, 10-15 minutes, rotating pan halfway through baking. Transfer sheet to wire rack and let tart cool completely, about 2 hours. (Cooked tart can be wrapped tightly in plastic and refrigerated for up to 24 hours.)

Remove outer metal ring of tart pan, slide thin metal spatula between tart and pan bottom, and carefully slide tart onto serving platter. Dust with extra confectioners’ sugar before serving.