Lemon Meringue Pie

Lemon Meringue Pie
recipe from The America's Test Kitchen Family Cookbook

Filling: 
1 1/2 cups cold water
1 cup sugar
1/4 cup cornstarch
1/8 tsp. salt
6 large egg yolks
1 Tb. grated lemon zest
1/2 cup fresh lemon juice (from about 3 lemons)
2 Tb. unsalted butter

Meringue:
1/3 cup water
1 Tb. cornstarch
4 large egg whites
1/2 tsp. vanilla extract
1/2 cup sugar
1/4 tsp. cream of tartar

1 pie crust, baked and cooled

1. Heat oven to 325 degrees.
2. Prepare the filling by combining sugar, water, cornstarch, and salt in large saucepan over medium heat and bring to a simmer, whisking constantly. When mixture starts to turn transluscent, whisk in egg yolks 2 at a time. Whisk in the zest, then the lemon juice, and finally the butter. Return the mixture to a full simmer, then remove the pan from the heat. Cover with plastic wrap, pressing onto the surface of the filling, to keep it hot while making the meringue.
3. Make the meringue by brining the water and cornstarch to a simmer in a small saucepan over medium-high heat, whisking constantly. When mixture turns translucent and begins to bubble, remove it from the heat.
4. Whip the egg whites and vanilla in a large bowl with an electric mixer on low speed until frothy. Mix sugar and cream of tartar together, then add to the egg whites, 1 tablespoon at a time. Increase speed to medium and whip the egg whites until soft peaks form. Add cooked cornstarch mixture to the whipped egg whites, 1 tablespoon at a time, and continue to whip the egg whites until they are glossy and form stiff peaks.
5. Remove plastic from the lemon filling and return to very low heat to reheat, about 1 minute. Pour the hot filling into the baked, cooled pie crust. Dollop the meringue over the top of the pie, making sure to adhere the meringue to the crust. Use the back of a spoon to create peaks in the meringue. Bake until the meringue is golden brown, about 20 minutes. Transfer the pie to a wire rack and cool to room temperature before serving.