1 1/4 cups granulated sugar, divided
1/3 cup cornstarch
4 cups whole milk
4 large eggs, separated and divided
1 teaspoon vanilla
1/4 teaspoon salt
2 tablespoons unsalted butter
1/4 teaspoon cream of tartar
1 11-ounce box nilla wafers
3-4 bananas, depending on size
Preheat oven to 350. Make custard: whisk 3/4 cup of the sugar, the cornstarch, milk and egg yolks in a pot set over medium heat, and cook, stirring constantly, until it just begins to bubble, 10 to 15 minutes. Turn heat down slightly, and allow mixture to simmer, still stirring constantly, for 1 minute, then remove mixture from heat. Whisk in vanilla, salt and butter.
Make meringue: put the egg whites, cream of tartar and 1/2 cup of sugar in the heatproof bowl of an electric mixer, and set over a medium saucepan of simmering water. Whisk until the sugar is dissolved and the mixture is hot to touch, about 3 minutes. Transfer to the stand mixer fitted with whisk, and beat until stiff, about 5 to 7 minutes.
Line a 13-by-9-inch oven-safe casserole pan with one layer of Nilla wafers and one layer of banana slices. (Reserve remaining Nilla wafers for a child or incident of depression.)
Pour the custard over the bananas and cookies, then use a spatula to spread the meringue. Bake in oven for 10 to 15 minutes, until the peaks are the color of a toasted marshmallow. Allow to rest until ready to serve.