In a large chilled mixing bowl, whip the cold heavy whipping cream on medium-high speed for 3-5 minutes until soft peaks form.

Gradually add the sweetened condensed milk to the whipped cream, continuing to mix for another 2-3 minutes until stiff peaks form.

Layer graham crackers at the bottom of a 9x13-inch baking dish, breaking them to fill gaps.

Spoon one-third of the whipped cream mixture over the graham cracker layer, spreading it evenly.

Add a layer of sliced mangoes over the whipped cream, distributing them evenly.

Repeat the layering process until all ingredients are used, finishing with a final layer of mango slices.

Cover with plastic wrap and refrigerate for at least 6 hours or overnight.

Slice into squares or rectangles and serve cold, garnished with extra mango slices or shredded coconut.