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 - Transfer the blended mixture into the Ninja Creami pint container. Seal tightly and freeze in an upright position for a minimum of 12 hours or overnight.
03 - In a mixing bowl, combine graham cracker crumbs, melted unsalted butter, and brown sugar. Mix together until the texture resembles wet sand, then set aside.
04 - When fully frozen, insert the pint container into the Ninja Creami appliance and run the 'Ice Cream' cycle according to manufacturer instructions.
05 - Create a 1-inch wide well in the center of the ice cream. Fill the cavity with the prepared graham cracker mixture.
06 - Reinsert the pint into the Ninja Creami and operate the 'Mix-In' function to thoroughly blend the graham cracker crumble into the ice cream.
07 - Scoop the finished ice cream into bowls. Garnish each serving with whipped cream and sliced bananas if desired. Serve immediately for optimal texture.