01 - Combine mashed bananas, whole milk, heavy cream, sweetened condensed milk, granulated sugar, vanilla extract, and salt in a blender. Blend until the mixture is completely smooth.
02 - Pour the blended mixture into a Ninja Creami pint container, seal, and freeze upright for a minimum of 12 hours or overnight until solid.
03 - Stir together graham cracker crumbs, melted butter, and brown sugar in a small bowl until the mixture resembles wet sand. Set aside.
04 - After the base is fully frozen, insert the pint into the Ninja Creami appliance and process using the 'Ice Cream' setting.
05 - Create a 1-inch wide well in the center of the ice cream. Spoon the graham cracker mixture into the well.
06 - Reinsert the pint and process again using the 'Mix-In' function until the graham cracker swirl is fully integrated.
07 - Scoop ice cream into individual bowls. Top with whipped cream and sliced bananas if desired. Serve immediately for optimal texture.