Preheat the oven to 375°F.
Place crust in a shallow 9-inch pie dish and pre-bake according to package directions.
Place egg yolks in a small bowl and beat them together. Set aside.
In a medium saucepan, whisk together the sugar, cornstarch, and salt. Add the egg yolks and mix until combined. Add the milk, lemon juice, and lemon zest. Bring the mixture to a boil over medium heat, stirring frequently. Boil for one minute, then remove from heat and stir in the butter and vanilla. Pour into the prepared pie crust.
Make the meringue by beating the egg whites and cream of tartar in a medium glass or metal bowl, until soft peaks form (3-5 minutes). Slowly add sugar, continuing to beat until glossy, stiff peaks form (about 2 minutes)
While the lemon filling is still warm, spread the meringue around the edge of the pie. Make sure the mixture attaches to the crust with no gaps. Add the remaining meringue to the center and use the back of a spoon to create small peaks all over the pie.
Bake at 325°F for about 20 minutes, or until the meringue is golden brown.