01 - Place 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 base into a Ninja Creami pint container. Seal tightly and freeze upright for at least 12 hours or overnight until solid.
03 - Combine graham cracker crumbs, melted butter, and brown sugar in a bowl. Mix until the texture resembles damp sand, then set aside.
04 - Once frozen, insert the pint into the Ninja Creami machine and process using the 'Ice Cream' preset.
05 - Create a 1-inch wide well in the center of the processed ice cream. Fill the well with the graham cracker mixture.
06 - Reinsert the pint into the machine and select the 'Mix-In' function to blend the graham cracker swirl into the base.
07 - Scoop the ice cream into individual bowls. Garnish with whipped cream and sliced bananas if desired, then serve immediately for optimal texture.