Combine graham cracker crumbs, butter and sugar in a medium bowl. Stir to combine. Press crumbs into the bottom and up the sides of a 9-inch pie dish. Bake 8-10 minutes until golden brown. Cool completely.
Sift together cornstarch and ¼ cup sugar into a medium bowl. Add egg yolks and mix well.
Bring milk, vanilla bean and the rest of the sugar (1/4 cup) to a low boil. Reduce heat. Remove vanilla bean.
Temper cream into yolks by slowly whisking a small amount of the hot milk mixture into the egg yolk mixture. Continue to slowly whisk in the milk making sure the eggs do not get too hot and begin to curdle.
Return to stove over medium-low heat and whisk until very thick.
Add banana puree and cool.
Poor into crust and cool at least 8 hours or overnight.
Whip cream to soft peaks and add sugar. Decorate top of pie with cream.