Instructions

FILLING

1. Bring the water, sugar, cornstarch, and salt to simmer in a large saucepan over medium heat, whisking constantly. When mixture starts to turn translucent, whisk in the egg yolks, 2 at a time. Whisk in lemon zest, juice and butter. Return the mixture to a brief simmer, then remove from the heat.
2. Pour the filling into a baked and cooled pie crust. Lay a sheet of plastic wrap directly on the surface of the filling and refrigerate the pie until the filling is cold, about 2 hours.

MERINGUE

1. Adjust your oven rack in the middle position and heat your oven to 400 degrees. Bring sugar and water to a vigorous boil, cook for 4 minutes (mixture will become slightly thickened and syrupy). Remove from the heat and set aside while beating the egg whites.
2. Using a stand mixer fitted with the whisk attachment, whip the egg whites, cream of tartar, and salt on medium-low speed until foamy, about 1 minute. Increase speed to medium-high and whip until soft peaks form, about 2 minutes. With mixer running, slowly pour hot syrup into whites (avoid pouring syrup onto whisk or it will splash). Add vanilla and beat until meringue has cooled and becomes very thick and shiny, 3 to 6 minutes.
3. Using a rubber spatula, mound the meringue over the filling, making sure the meringue touches the edges of the crust. Use the spatula to create peaks all over the meringue. Bake until the peaks turn golden brown, about 6 minutes. Transfer to a wire rack and let cool to room temperature.