In a small mixing bowl, whisk together the sugar, flour, and salt.
In a separate large mixing bowl, whisk the evaporated milk, egg yolks, and half and half until well combined.
Add the dry ingredients to the wet, whisking until well combined. The sugar should start to dissolve as you whisk.
Pour the mixture into a large saucepan and bring up to simmer over medium-high heat, stirring often. Once it starts to steam, reduce to medium heat.
Continue to cook, constantly stirring, until the custard has thickened enough to stick to a spoon. Once thickened, immediately remove from heat and whisk in the butter and vanilla. Set aside.
Make the Meringue
Place the 6 egg whites in a large mixing bowl. Using an electric mixer, beat on high until they become frothy and foam.
Mix in the cream of tartar, then gradually add the sugar, continuing to beat until sugar dissolves and stiff peaks form.
Assemble and Bake
Preheat oven to 325˚ F.
Spray a 9x13 casserole dish with nonstick cooking oil. Place a layer of vanilla wafers across the bottom, covering all available space. Top the cookies with an even layer of banana slices. Spread ½ of the pudding over the top, then repeat - adding another layer of wafers, followed by bananas, and finally the remaining pudding.
Spread meringue over pudding, making as many peaks as possible.
Place the baking dish into the preheated oven for 25 to 30 minutes - until the meringue has browned slightly.
Remove from oven and allow to cool. It may be served warm or cold; chill in the refrigerator until the desired temperature is reached.
Be sure to keep cooking the pudding until the desired thickness is reached. It will cool quickly and will not thicken any more once you turn off the heat.
When whipping the meringue, keep it going until you have stiff peaks. It may be tempting to stop a little early, but you want to take it a little further than you would whip cream.
How long you bake the dish is really a personal preference. I recommend cooking until the peaks have browned for the most toasty flavor. But some will choose a less-cooked meringue, and both are fine.
Can I substitute regular milk for condensed milk? Yes, but you will sacrifice some of the richness and lots of the flavor that condensed milk gives.Can I use non-dairy milk? While we have not yet tested the use of milk alternatives, the thickening of the pudding comes from the flour, so I would guess that it would work.If I don't want to use the meringue topping, can I skip the baking step? Yes, all the ingredients inside the pudding are fully cooked except for the meringue. So, if you opted to add something like whipped cream and cookie crumbles, you could skip the baking.