FOR THE CRUST: Whisk together yolk, cream, and vanilla in small bowl; set aside. Pulse flour, sugar, and salt in food processor until combined, 2 pulses. Scatter butter pieces over flour mixture; pulse to cut butter into flour until mixture resembles coarse meal, about 15 pulses. With machine running, add egg mixture and process until dough just comes together, about 25 seconds. Turn dough onto sheet of plastic wrap and press into 6-inch disk. Wrap in plastic and refrigerate at least 2 hours.

Unwrap dough; lightly flour large sheet of parchment paper or plastic wrap and place dough in center. Roll into a 15-inch circle, then loosen the dough from plastic and flour again. Ease dough over rolling pin and roll it up loosely. Unroll dough on top of tart pan. Lift edges of dough with your hand and ease it into corners of the pan with your other hand. Press dough into fluted sides, forming a distinct seam along pan circumference. Run rolling pin over top of pan to remove excess dough. Freeze dough 30 minutes.

Meanwhile, adjust one oven rack to upper-middle position and other rack to lower-middle position; heat oven to 375 degrees. Place chilled tart shell on baking sheet; line tart shell with aluminum foil and fill with pie weights. Bake on lower rack 30 minutes, rotating halfway through baking. Remove foil and weights. Transfer baking sheet with tart shell to upper rack and continue to bake until shell is golden brown, about 5 minutes longer.

FOR THE LEMON FILLING: Whisk yolks and whole eggs together in medium bowl until combined, about 5 seconds. Add sugar and whisk until just combined, about 5 seconds. Add lemon juice, zest, and salt; whisk until combined, about 5 seconds. Transfer mixture to medium saucepan, add butter pieces, and cook over medium-low heat, stirring constantly with wooden spoon, until curd thickens to thin saucelike consistency and registers 170 degrees, about 5 minutes. Immediately strain curd through fine-mesh strainer set over bowl. Stir in heavy cream; pour curd into warm tart shell immediately.

Bake until filling is shiny and opaque and until the center 3 inches jiggle slightly when shaken, 10 to 15 minutes. Cool on wire rack to room temperature, about 45 minutes. Remove outer metal ring of tart pan, slide thin metal spatula between tart and pan bottom to release, and carefully slide tart onto serving platter. Cut into wedges and serve.