Step 1

Stir together graham cracker crumbs, melted butter, and sugar in a medium bowl; set 1 tablespoon graham cracker mixture aside.

Step 2

Stir together condensed milk, lime zest and juice, vanilla, and salt in a large bowl; set aside. Beat cream in a separate large bowl with an electric mixer fitted with a whisk attachment on high speed until stiff peaks form, 2 minutes. Fold whipped cream and remaining graham cracker mixture in bowl into condensed milk mixture.

Step 3

Spoon into a 9- x 5-inch loaf pan. Sprinkle with reserved 1 tablespoon graham cracker mixture. Cover; freeze until firm, about 6 hours.