01 - Combine mashed bananas, whole milk, heavy cream, sweetened condensed milk, granulated sugar, vanilla extract, and salt in a blender and blend until completely smooth.
02 - Pour the blended mixture into the Ninja Creami pint container, seal, and freeze upright for at least 12 hours or overnight.
03 - In a mixing bowl, stir together graham cracker crumbs, melted unsalted butter, and brown sugar until the mixture resembles wet sand. Reserve.
04 - When the ice cream base is fully frozen, place the pint in the Ninja Creami and process using the 'Ice Cream' setting.
05 - After the first spin, create a 1-inch well in the center of the ice cream and fill with the graham cracker crumble.
06 - Reinsert the pint into the Ninja Creami and process on the 'Mix-In' setting until the swirl is thoroughly distributed.
07 - Scoop into bowls and garnish with whipped cream and sliced bananas if desired. Serve immediately.