Crush your graham crackers in a zipper bag until medium coarse crumbs form, add melted butter and mix mixture around well.
Spray your muffin pan with nonstick cooking spray and divide the graham crackers evenly into 12 and press down on the muffin pan, allowing the crumb topping to go slightly above the sides. Place in freezer for 20 minutes.
To make the custard, add the sugar, cornstarch, salt, milk and egg yolks in a medium sauce pan. Stir custard over medium heat and keep stirring until it gets thick around 5-7 minutes. You'll know when it's done and coats your spoon. Turn off hea, add the vanilla extract and mix that in.
Take your muffin tin pan out of the freezer and ladle the custard into each graham cracker crust evenly. Cover loosely with plastic wrap and place muffin tin pan in the refrigerator for at least 5 hours.
Before serving, add your heavy cream to a bowl and use a hand mixer (or stand mixer). Mix on medium-high speed until thick and then add vanilla and the powdered sugar and keep mixing until whipped cream forms as soft peaks. Don't over beat or the cream will curdle!
Slice your two bananas and divide evenly into 12 servings. Before serving, top each pie with whipped cream and the sliced bananas. Serve immediately.
The pies without the cream and bananas can be made a day ahead and kept in the refrigerator. Top with whipped cream and sliced bananas before serving.