01 - Combine mashed bananas, whole milk, heavy cream, sweetened condensed milk, granulated sugar, vanilla extract, and salt in a blender. Blend until completely smooth.
02 - Transfer blended mixture into the Ninja Creami pint container. Seal tightly and freeze upright for at least 12 hours, preferably overnight.
03 - Mix graham cracker crumbs, melted butter, and brown sugar in a small bowl until the mixture resembles damp sand. Set aside.
04 - Place the frozen pint into the Ninja Creami machine and process using the 'Ice Cream' function according to manufacturer’s instructions.
05 - After the first spin, use a spoon to create a 1-inch well in the center of the ice cream and pour the graham cracker crumble into the well.
06 - Return the pint to the machine and process with the 'Mix-In' setting until the crumble is fully incorporated.
07 - Scoop the finished ice cream into bowls. Top with whipped cream and sliced bananas if desired. Serve immediately.