Make the filling: In a small bowl combine milk, egg yolks and lime juice; whisk until smooth. If you are using your own homemade graham cracker pie crust, bake the crust before adding the filling for about 7 minutes.
Bake filling in crust: Pour filling into store-bought or your homemade graham cracker crust (link below in notes) bake at 350º for 10 minutes.
Make meringue topping: While baking, make meringue topping. In the bowl of a mixer, add the egg whites, vanilla and cream of tartar. Beat the egg whites on medium speed until soft peaks form.
Slowly add sugar: Add the sugar, 1 tablespoon at a time, while beating on high speed. Continue beating on high speed until the sugar dissolves and stiff, glossy peaks form. When you lift the beaters, the tips will stand straight up.
Use a spatula to cover filling: Let the pie cool down after you remove from the oven. Spread the meringue over the pie and bake at 350º for about 5-8 minutes. Keep an eye on the meringue so it doesn't burn. (I sometimes broil the topping. If you choose to broil, it won't take more than 3-4 minutes and you have to carefully watch it because it could be perfect one minute and burned the next).
Chill pie before serving: Cool pie completely on rack (filling will set as it cools), then chill, covered, at least 8 hours. Slice, serve and enjoy!