In a saucepan on low heat, heat 1 cup milk, 2 cups whipping cream, 3/4 cup sugar and butter
In another bowl, cream together egg yolks and 1/2 cup sugar and whisk into hot cream mixture
Allow mixture to cook, stirring frequently, until it starts to thicken (make sure heat is very low)
Mix reserved milk and cornstarch together and slowly whisk into the hot mixture
Whisking constantly, making sure to blend bottom and sides, and continue cooking until mixture is a thick pudding then remove from heat
As the pudding starts to cool, place plastic wrap on top to avoid filming then continue cooling in fridge
Slice bananas an toss with lemon juice and pat dry with a paper towel
Line bananas on top of cooled ganache then pour cooled pudding over top and place in fridge to continue cooling