1. Prepare the Pie Crust:

1. Preheat your oven to 375°F (190°C).
2. Place the pie crust in a 9-inch pie plate and bake according to package instructions or until golden brown. Allow it to cool completely.

2. Prepare the Butterscotch Filling:

1. In a medium saucepan, whisk together brown sugar, cornstarch, and salt.
2. Slowly whisk in the whole milk to make sure the mixture is smooth.
3. Cook over medium heat, stirring constantly, until the mixture thickens and begins to boil.
4. In a separate bowl, lightly beat the egg yolks. Gradually add a small amount of the hot mixture to the egg yolks, whisking constantly, to temper them.
5. Slowly pour the tempered egg yolks back into the saucepan, stirring constantly. Cook for another 2 minutes.
6. Remove from heat and stir in butter and vanilla extract until the butter melts and the mixture is smooth.

3. Prepare the Meringue Topping:

1. In a clean bowl, beat the egg whites with cream of tartar until soft peaks form.
2. Gradually add the granulated sugar, continuing to beat until stiff peaks form.

4. Assemble and Bake the Pie:

1. Pour the butterscotch filling into the cooled pie crust, spreading it evenly.
2. Spread the meringue over the filling, making sure it touches the edges of the crust to prevent shrinking.
3. Bake in the preheated oven at 375°F (190°C) for 10-12 minutes, or until the meringue is golden brown.

5. Cool and Serve:

1. Allow the pie to cool to room temperature before refrigerating for at least 2 hours to set the filling.
2. Slice and serve chilled for the best texture and flavor.