Peel the mangoes and slice them into thin strips for layering. Set aside a handful of the most even, attractive slices for the top layer of the dessert.

In a chilled mixing bowl, beat the cold heavy cream using an electric mixer until soft peaks form—about 3 minutes. Slowly pour in the sweetened condensed milk, add vanilla extract if using, and a pinch of salt. Continue whipping until the mixture becomes smooth and fluffy (but not stiff)—this should take another 2-3 minutes.

Arrange whole graham crackers in a single layer at the bottom of an 8×8-inch glass or ceramic dish, breaking crackers as needed to fill gaps evenly.

Spoon and spread a generous layer of the whipped cream mixture over the graham cracker base, smoothing the surface with a spatula.

Lay mango slices in a single, even layer over the cream, using enough to mostly cover the surface.

Spread another layer of the whipped cream mixture over the mangoes, completely covering the fruit.

Arrange the reserved mango slices neatly on top for presentation. Optional: sprinkle with crushed graham crackers.

Cover the dish tightly with plastic wrap and refrigerate for at least 6 hours, or overnight.