Make the Crust : Preheat your oven to 350°F (175°C) and line an 8x8-inch baking pan with parchment paper, leaving a slight overhang for easy removal. In a bowl, combine the graham cracker crumbs, brown sugar, and melted butter. Mix until the texture resembles wet sand. Press the mixture evenly into the bottom of the prepared pan to form the crust. Bake for 10 minutes, then remove from the oven and let it cool while you prepare the filling.
Prepare the Filling : In a large mixing bowl, beat the cream cheese until smooth and creamy. Add the sweetened condensed milk and mix until fully combined. Stir in the sour cream, vanilla extract, and mashed bananas, mixing until smooth.
Assemble and Bake : Pour the banana cheesecake filling over the cooled crust, spreading it evenly. Bake in the preheated oven for 30 minutes, or until the edges are set and the center has a slight jiggle. Remove from the oven and allow to cool at room temperature for about 30 minutes.
Chill and Serve : Transfer the cheesecake to the refrigerator and chill for at least 2 hours, or until fully set. Use the parchment paper overhang to lift the cheesecake out of the pan. Cut into squares. Serve as is, or garnish with whipped cream, banana slices, or crushed graham crackers for extra flair.