01 - In a mixing bowl, whip the chilled heavy cream with an electric mixer on medium-high speed until soft peaks form.
02 - Gently fold in the sweetened condensed milk until well combined and smooth.
03 - Arrange a single layer of graham crackers in the bottom of a 9x13-inch glass dish, breaking crackers as needed to fit the surface.
04 - Spread one-third of the cream mixture evenly over the graham crackers.
05 - Layer with one-third of the sliced mangoes, distributing them evenly across the cream.
06 - Repeat the layering process twice more: graham crackers, cream, then mangoes. Finish with a final layer of mangoes on top.
07 - Sprinkle reserved graham cracker crumbs over the top for garnish, if desired.
08 - Cover the dish with plastic wrap and refrigerate for at least 6 hours, or overnight, until completely set and chilled.
09 - Slice into squares and serve cold. Garnish with fresh mint leaves if desired.