Make the Tart Shell

1. Preheat your oven to 350°F.
2. In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and sugar until just combined. Add the vanilla.
3. In a separate bowl, sift together the flour and salt, then slowly add to the butter mixture on low speed. Mix until the dough begins to come together.
4. Turn the dough out onto a floured surface, shape into a flat disk, and press it into a 10-inch round or 9-inch square tart pan with a removable bottom. Make sure the edges are even. Chill until firm.
5. Butter one side of a square of aluminum foil and press it into the chilled tart shell. Fill with beans or rice to weigh it down. Bake for 20 minutes.
6. Remove the foil and weights, prick the tart all over with a fork, and bake for another 20–25 minutes, or until lightly browned. Let cool to room temperature.

Make the Lemon Curd

1. Zest the lemons, being careful to avoid the bitter white pith. Squeeze the lemons to yield ½ cup juice.
2. In a food processor, combine the zest and sugar. Pulse for 2–3 minutes until the zest is finely minced.
3. In the bowl of a stand mixer, cream the butter with the lemon sugar mixture. Add the eggs one at a time, followed by the lemon juice, vanilla, and salt. Mix until smooth.
4. Pour the mixture into a saucepan and cook over low heat, stirring constantly, until it thickens (about 10 minutes). The curd should reach 175°F but not simmer. Remove from heat.
5. Pour the warm lemon curd into the tart shell and let it set at room temperature.

Make the Italian Meringue

1. In a small saucepan, combine sugar and water. Bring to a boil over high heat, stirring just until dissolved, then stop stirring. Cook until the syrup reaches 240°F on a candy thermometer.
2. Meanwhile, in the bowl of a stand mixer fitted with a whisk attachment, beat the egg whites and cream of tartar on medium speed until soft peaks form (about 2 minutes).
3. With the mixer running, slowly drizzle in the hot sugar syrup. Be cautious—hot sugar is no joke.
4. Increase the mixer speed to high and whip until the meringue reaches your desired stiffness.

Assemble the Tart

1. Once the lemon curd is set, pipe or dollop the Italian meringue over the top in whatever dramatic style you prefer. I did a twisty thing on the tart photographed here. 
2. Optional but fabulous: Use a kitchen torch to toast the meringue for a golden finish.