01 - Combine mashed bananas, whole milk, heavy cream, sweetened condensed milk, granulated sugar, vanilla extract, and salt in a blender. Process until the mixture is completely smooth.
02 - Pour the blended mixture into the Ninja Creami pint container. Seal tightly and freeze upright for at least 12 hours or overnight.
03 - In a mixing bowl, combine graham cracker crumbs, melted unsalted butter, and brown sugar. Stir until the texture resembles wet sand. Set aside.
04 - Once the base is fully frozen, insert the container into the Ninja Creami machine and process using the 'Ice Cream' setting.
05 - After the initial spin, create a 1-inch well in the center of the ice cream. Add the graham cracker mixture into the well.
06 - Reinsert the pint into the Ninja Creami and run the 'Mix-In' function until the graham swirl is fully incorporated.
07 - Scoop the finished ice cream into serving bowls. Top with whipped cream and sliced bananas if desired. Serve immediately.