Preheat your oven to 325°F (160°C). Line a 9x9 inch baking dish with parchment paper. In a medium bowl, mix together the graham cracker crumbs, 1/4 cup sugar, and melted butter until combined.
Press the mixture into the bottom of the prepared baking dish.
In another bowl, beat the cream cheese and 1 cup sugar until smooth.
Add the eggs, one at a time, beating well after each addition.
Stir in the vanilla extract, sour cream, and flour until smooth. Fold in the mashed bananas.
Pour the cream cheese mixture over the graham cracker crust in the baking dish.
Bake for 40-45 minutes, or until the edges are set and the center is slightly jiggly. Remove from the oven and let it cool completely.
In a separate bowl, whisk together the instant banana pudding mix and milk until thickened.
Spread the pudding mixture over the cooled cheesecake layer.
Cover and refrigerate for at least 4 hours, or until set.
Once chilled, slice into squares and serve with whipped cream and banana slices if desired.