Mix the graham cracker crumbs, 1/2 cup sugar, melted butter, and cinnamon in a bowl. Reserve 1/4 cup for topping the pie. Press the remaining crumb mixture in the bottom and up the sides of a 9-inch deep-dish pie plate. Bake the crust in the preheated oven for 8 minutes.
Heat the milk in a saucepan over medium-high heat. In a non-plastic bowl, whisk together the 1/2 cup sugar, cornstarch, egg yolks, and vanilla. When the milk is hot but not boiling, slowly pour the milk in a steady stream into the yolk mixture, whisking constantly. Return the custard to the saucepan and bring to a boil over medium heat, stirring constantly with a wooden spoon or a heat-proof spatula. Cook and stir for 2 to 3 minutes over low heat until the custard has thickened. Pour the custard into the graham cracker crust.
Preheat the oven’s broiler and set the oven rack about 6 inches from the heat source.
Beat the egg whites until medium peaks form; add 2 tablespoons of sugar and beat until the meringue is stiff. Scoop out the meringue on top of the custard filling. Sprinkle the meringue with the reserved graham cracker crumbs.
Place the pie under the broiler and bake until the meringue starts to brown, 3 to 5 minutes.