Pre-bake pie crust according to package directions.
Let Cool. Set aside.
Leave oven on and set temperature to 350.
In a medium Sauce pan, add all filling ingredients except for egg yolks and butter.
Stir to combine.
Cook over low heat, whisking continuously until it begins to bubble.
Add butter and whisk until melted and combined.
Remove from heat.
Add 1/2 cup of warm mixture to egg yolks to temper. Stir until blended.
Add egg yolk mixture back to filling pan and whisk to incorporate.
Return to low heat.
Whisk constantly until mixture is thickened to custard consistency.
Pour filling into baked pie shell.
Combine egg whites and cream of tartar in a large bowl or stand mixer.
Whip at low speed to begin aerating.
Increase to medium when whites are foamy.
Continue whipping and add sugar, one tablespoon at a time.
Increase speed to medium high and whip until stiff peaks form.
Use a spatula and cover pie filling completely.
Take care to insure that meringue adheres to crust around the edges.
Bake for about 10 minutes until peaks of meringue are browned.
Remove from oven and allow to cool for 1 hour.
Refrigerate uncovered for at least 3 hours before serving.