Crust: either make a regular baked pie crust, or make/purchase a graham cracker pie crust.
1/2 cup sugar1 Tbsp. flour (rounded)
2 Tbsp. cornstarch1/2 tsp salt
2 cups milk1 egg yolk
1 tsp. vanilla
Mix together dry ingredients. Add milk and mix with whisk. Cover with waxed paper. Microwave 4-5 minutes until boiling, stopping every minute to stir it. Slightly beat the egg yolk. Add about 1/2 cup of microwaved mixture to egg yolk and mix, then add that mixture back to the bowl. Microwave one more minute. Then add vanilla. Stir. Cover with a new piece of waxed paper, pushing the wax paper down to touch the top of the custard (this will make it so the custard doesn't get a crusty top). Refrigerate for about 4 hours.
To make banana cream pie: Cut banana slices into the bottom of the crust. Fill pie with custard. Top with Cool Whip if desired.