01 - Pour chilled heavy cream into a mixing bowl. Using an electric mixer on medium-high speed, whip until soft peaks form.
02 - Gently fold sweetened condensed milk into the whipped cream until fully incorporated and smooth.
03 - Arrange graham crackers in a single layer at the bottom of a 9x13-inch glass dish. Break crackers as needed to fit the space completely.
04 - Spread one-third of the cream mixture evenly over the graham cracker base using a spatula.
05 - Distribute one-third of the sliced mangoes evenly over the cream layer.
06 - Create two more complete layers in the same order: graham crackers, cream mixture, then mango slices.
07 - Finish with a top layer of mango slices. Sprinkle graham cracker crumbs over the surface as garnish if desired.
08 - Cover the dish tightly with plastic wrap. Refrigerate for at least 6 hours or overnight until the dessert is fully set and chilled.
09 - Cut into squares or rectangles. Serve cold and garnish with fresh mint leaves if using.