4 extra-large egg whites, at room temperature
1/4 tsp cream of tartar
1/4 tsp salt
1/2 cup sugar
Whip the egg whites, cream of tartar, and 1/4 teaspoon salt with the whisk attachment of your mixer on high speed until frothy. With the mixer still running, slowly add the remaining 1/2 cup of sugar and beat until the meringue is thick and shiny, about 2 minutes.
1/4-pound (1 stick) unsalted butter, at room temperature
1 1/2 cups sugar
4 extra-large eggs
3 extra-large egg yolks (save the whites for the meringue)
1/4 cup finely grated lemon zest (6 to 8 lemons if small 4-6 if large)
1/2 cup freshly squeezed lemon juice
1/8 tsp salt
Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment for 1 minute. On low speed, add the eggs and egg yolks one at a time, and then add the lemon zest, lemon juice, and salt. Don't worry; it will look curdled. Pour the mixture into a small saucepan and cook over medium-low heat for 8 to 10 minutes, until thick, stirring constantly with a wooden spoon. Whisk briskly when it starts to thicken and cook over low heat for 1 to 2 minutes, whisking constantly. Don't allow it to boil! It will be 175° F on a thermometer. Pour into a bowl and cool to room temperature.
Assembling the tart:
Prepare your favorite flaky pie crust or use a refrigerated dough. Roll crust onto a tart pan with removable sides. Be careful not to stretch dough as it will spring back when baking and leave your tart misshapen. Press dough into sides of pan then run a rolling pin across the top to cut off the excess dough. Bake crust using directions for the recipe or refrigerated crust you are using be sure to prick bottom of crust with a fork so the steam escapes. Once crust is baked to a golden brown, allow to cool to room temperature. Once cooled fill with lemon filling and spread evenly to sides. Place meringue in a pastry bag fitted with a star tip and pipe meringue onto the tart in whatever pattern you like. Make sure to completely cover the filling and pie crust edges with the meringue! Bake in oven preheated to 425° F for about 8 minutes until meringue is browned on top. Remove from oven and allow to cool to room temperature.
Personally, I like my lemon meringue chilled so I place it in the refrigerator before serving.