To make lemon curd: Whisk together 1 egg, 2 egg whites, 3/4 cup sugar, lemon juice and zest in a heavy-bottomed, medium saucepan. (If you do not have a heavy-bottomed pan, use a double boiler and increase the cooking time slightly.) Add butter and cook over medium-low heat, whisking constantly, until thickened, 5 to 7 minutes. (The curd will become thicker as it cools.) Transfer to a bowl and let cool. Cover and refrigerate until chilled.

To make pastry shells: Place oven rack in the upper third of the oven; preheat to 375 degrees F. Lightly oil 24 three-inch muffin cups or coat them with cooking spray.

Combine water, oil, 2 tablespoons sugar and salt in a medium saucepan; bring just to a boil over medium heat. Remove from the heat and add flour all at once. Stir with a wooden spoon until the mixture forms a smooth mass. Let cool for 2 minutes, then transfer to a stand-up mixer fitted with paddle attachment or to a food processor.

Whisk together 2 eggs, 4 egg whites and vanilla in a measuring cup. Gradually add one quarter of the egg mixture to the flour paste, beating or processing until the eggs are incorporated. Repeat with 3 more additions of the egg mixture until the batter just falls from a spoon. (The batter may seem lumpy.)

Place about 1 tablespoon pastry into each prepared muffin cup. Dip a spoon in cold water and press the pastry into the sides of the cups. With moistened fingers, press the pastry partway up the sides of the cups, forming 3/8-inch-thick shells.

Bake for 5 minutes. Remove from the oven and prick the centers of the shells with a fork. Return to the oven and bake until puffed and golden, 10 to 15 minutes longer. Loosen shells with a table knife or small metal spatula and transfer to a wire rack. Let cool.

To assemble tartlets: Not more than 1 1/2 hours before serving, spoon about 1 tablespoon lemon curd into each tartlet shell and dust with confectioners' sugar.