Prepare the mangoes: Peel the mangoes and slice them thinly. Set aside.
Whip the cream: In a large bowl, whip the chilled heavy cream to soft peaks. Slowly fold in the sweetened condensed milk until smooth and creamy.
Layer the dessert: In an 8x8-inch glass dish, arrange a layer of whole graham crackers to cover the bottom.
Add cream: Spread a layer of the whipped cream mixture evenly over the graham crackers.
Add mangoes: Arrange a single layer of mango slices over the cream.
Repeat layers: Continue layering graham crackers, cream, and mangoes until the dish is filled, ending with a cream layer on top.
Top with garnish: Garnish the top layer with sliced mangoes arranged decoratively and a sprinkle of crushed graham crackers.
Chill: Cover with plastic wrap and refrigerate for at least 6 hours, preferably overnight, to let the layers set and soften.
Serve: Slice into portions and serve chilled.