In a large mixing bowl, whip the heavy cream until soft peaks form.
In another bowl, combine the sweetened condensed milk, fresh lemon juice, lemon zest, vanilla extract, and salt. Mix until smooth.
Gently fold the whipped cream into the lemon mixture until fully combined, being careful not to deflate the whipped cream.
In a separate bowl, mix the crushed graham crackers with the melted butter until well combined.
In serving glasses or a dish, layer the graham cracker mixture at the bottom, followed by a layer of the lemon cream mixture. Repeat the layers until the glasses are filled, finishing with the lemon cream on top.
Cover and refrigerate for at least 2 hours to allow the flavors to meld and the cream to set.
Before serving, garnish with fresh berries if desired.