Sweet pastry dough for a single-crust pie
1/2 Cup heavy cream
1/2 Cup plus 1 Tbsp sugar
1 tsp finely-grated fresh lemon zest
1/2 Cup fresh lemon juice
4 large egg yolks
1 whole large egg
a 9-1/2″ round fluted tart pan (1 inch deep) with a removable bottom;
pie weights or raw rice;
a small (culinary) blowtorch
Using a lightly-floured rolling pin on a lightly-floured surface, roll out dough into a 13-inch round. Gently fit into the tart pan and trim any edges that stick out. Chill pastry shell until dough is firm, about 30 minutes.
Meanwhile, put oven rack in middle position and preheat oven to 375°F.
Lightly prick bottom of chilled pastry shell all over with a fork. Now line the crust-filled tart pan with aluminum foil and top foil with pie weights to keep crust from “bubbling” up. Put tart pan in the oven and bake until sides are set and the edge is a pale golden color, 18 to 20 minutes. Now carefully remove foil and weights, and continue to bake pastry shell until it turns a deep golden color, another 15 to 20 minutes more. Remove tart pan from oven, and reduce oven temperature to 300°F.
Using an electric mixer fitted with the whisk attachment, whisk together in a mixing bowl the cream, 1/2 Cup sugar, lemon zest and juice, egg yolks, and additional whole egg until all ingredients are thoroughly combined.
Put tart shell (still in the tart pan) onto a large baking sheet and transfer to 300°F oven. With oven rack extended, carefully pour creamy lemon filling into tart shell (custard will still have bubbles on top), then carefully slide rack back into oven.
Bake tart until custard is “set” (mostly firm) 3 inches in from edge, but trembles slightly in center when gently jiggled, 25 to 35 minutes. Remove tart pan from baking sheet, and cool the tart, still in the pan, on a wire cooling rack for at least 30 minutes. Carefully remove outside of the tart pan and allow tart to continue cooling, to room temperature, about 1-1/4 hours.
Just before serving, sprinkle remaining 1 Tbsp sugar evenly over the top of the tart. Using your lighted culinary blowtorch, move the flame evenly back and forth, just above the top of the tart, avoiding the crust, until the sugar is caramelized and slightly browned (be careful not to burn the sugar!). Allow tart to stand 5 minutes before serving.
MAKE AHEAD: The tart, without the caramelized-sugar top, can be baked and cooled up to 1 day ahead, then chilled in an airtight container. When ready to finish and serve, very gently blot any moisture from the surface of the tart with paper towels, just before sprinkling with sugar and caramelizing top.