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 - Pour the blended mixture into the Ninja Creami pint container. Seal tightly and position upright in the freezer for at least 12 hours or overnight to ensure full freezing.
03 - Stir together graham cracker crumbs, melted unsalted butter, and brown sugar in a small bowl until the consistency resembles wet sand. Set aside until ready to use.
04 - Once frozen, insert the pint container into the Ninja Creami ice cream maker and process using the 'Ice Cream' function according to manufacturer instructions.
05 - After the first spin, create a 1-inch wide well in the center of the ice cream. Pour in the prepared graham cracker crumble.
06 - Reinsert the container and use the 'Mix-In' program to evenly distribute the crumble throughout the ice cream.
07 - Portion the finished ice cream into bowls and, if desired, garnish with whipped cream and sliced bananas. Serve immediately for best texture.