cream pie... rich but not heavy?
imho, you DO want the custard to be thick in a banana cream pie, or when you cut it, it will simply ooze and loose it's shape, which to me is the fun about eating pie, otherwise bake it in a custard cup.
I make a stirred stovetop custard and use plenty of cornstarch. It will be silky smooth and if you use a fresh vanilla bean in the scalded milk, it'll be delicious.
I use the same custard when making a trifle.
One of the best recipes for Banana Cream Pie is from Jim Dodge's American Baker. His pastry cream has only one egg and is very light, perfect for the bananas. His pie is mostly bananas with just enough pastry cream folded in to coat them. Here is a paraphrase of his recipe:
1/4 cup sugar
1 TB flour
2 tsp cornstarch
1 large egg
1 cup whole milk
3 TB butter, room temperature
1/2 tsp vanilla extract (increased his recipe)
Mix together the sugar, flour and cornstarch. Beat in the egg until well mix and light. I use a wooden spoon. Heat milk to a boil and temper the flour/egg mixture. Cook mixture over medium heat, whisk vigorously and continuoulsy until mixture bubbles and thickens. Remove from heat and whisk in butter and vanilla. Cool with with a plastic wrap on top of the pastry cream.
A 10 inch fully baked pie shell; 6 large ripe/firm bananas thickly sliced folded into the cooled pastry cream; 2 cups of whipping cream (whipped with a little sugar).