Preheat your oven to 350°F (175°C). In a medium bowl, combine the graham cracker crumbs, 1/4 cup sugar, cinnamon, and melted butter until the mixture resembles wet sand.

Reserve 2 tablespoons of the graham cracker mixture for garnish, then press the remaining mixture firmly into the bottom and up the sides of a 9-inch pie plate. Bake the crust for 8 minutes until slightly golden and fragrant, then set aside to cool.

In a medium saucepan, whisk together 1/2 cup sugar, cornstarch, and salt. Gradually whisk in the whole milk and egg yolks until the mixture is smooth and completely combined.

Place the saucepan over medium heat and cook, stirring constantly with a whisk to prevent lumps, for about 6 to 8 minutes until the mixture thickens significantly and begins to bubble. Remove from heat immediately, then stir in the vanilla extract and 1 tablespoon of butter until fully melted and smooth.

Pour the hot vanilla custard into the baked graham cracker crust, smoothing the top with a spatula. Place a piece of plastic wrap directly onto the surface of the custard to prevent a skin from forming while you prepare the meringue.

In a clean glass or metal bowl, beat the egg whites and cream of tartar with an electric mixer on medium-high speed until soft peaks form, which takes about 2 minutes.

Gradually add the remaining 6 tablespoons of sugar, one tablespoon at a time, beating constantly on high speed until stiff, glossy peaks form and the sugar is fully dissolved.

Remove the plastic wrap from the custard. Spread the whipped meringue over the hot filling, ensuring you spread it all the way to the edge of the crust to seal it and prevent shrinking, then sprinkle the reserved graham cracker crumbs over the top.

Bake at 350°F (175°C) for 10 to 12 minutes, or until the meringue peaks are beautifully golden brown. Allow the pie to cool completely at room temperature for 1 hour, then chill in the refrigerator for at least 2 hours before slicing and serving.