1. Preheat your oven to 350°F (175°C).

2. In a medium bowl, combine graham cracker crumbs, granulated sugar, and melted butter. Mix well until crumbs are evenly moistened.

3. Press the mixture firmly and evenly into the bottom and up the sides of a 9-inch pie plate.

4. Bake for 8-10 minutes, or until lightly golden brown. Let cool completely on a wire rack while you prepare the filling.

5. In a medium saucepan, melt the butter over medium heat.

6. Stir in the brown sugar, cornstarch, and salt. Cook, stirring constantly, for 2-3 minutes until the mixture forms a thick, sandy paste and is fragrant. This step deepens the butterscotch flavor.

7. Gradually whisk in the milk and heavy cream. Bring the mixture to a gentle boil over medium heat, continuing to whisk constantly to prevent scorching. Boil for 1 minute, still whisking, until thickened.

8. In a separate small bowl, whisk the egg yolks. Slowly drizzle about ½ cup of the hot butterscotch mixture into the egg yolks, whisking continuously. This tempers the eggs, preventing them from scrambling.

9. Pour the tempered egg yolk mixture back into the saucepan with the remaining butterscotch mixture. Cook over medium-low heat, whisking constantly, for another 1-2 minutes until the filling is very thick and coats the back of a spoon. Do not boil once the egg yolks are added.

10. Remove from heat and stir in the vanilla extract. For an ultra-smooth filling, pour the butterscotch through a fine-mesh sieve into a clean bowl.

11. Pour the hot butterscotch filling into the cooled graham cracker crust.

12. Place a piece of plastic wrap directly onto the surface of the filling to prevent a skin from forming. Chill the pie in the refrigerator for at least 4-6 hours, or preferably overnight, until thoroughly set.

13. In a large, very clean mixing bowl (ensure no grease), beat the egg whites with an electric mixer on medium speed until foamy.

14. Add the cream of tartar (if using) and continue beating until soft peaks form.

15. Gradually add the granulated sugar, 1 tablespoon at a time, while continuing to beat on high speed. Beat until stiff, glossy peaks form and the sugar is fully dissolved (test by rubbing a small amount between your fingers; it should feel smooth).

16. Beat in the vanilla extract for a final 30 seconds.

17. Remove the chilled pie from the refrigerator. Spoon or pipe the meringue onto the chilled filling, spreading it all the way to the edges of the crust to seal it and prevent weeping. Create decorative swirls with the back of a spoon or a piping bag.

18. Lightly brown the meringue using a kitchen torch. Alternatively, place the pie under a broiler for 1-2 minutes, watching carefully to prevent burning.

19. Serve immediately or chill for another 30 minutes to set the meringue.