Pulse the biscuits in a food processor until finely crushed but not powdery. Reserve 1/3 cup for the topping.
Whip the Cream:
Beat the cold cream to soft peaks. Add condensed milk, vanilla, and salt, then beat briefly to medium peaks. Do not overwhip.
Layer and Chill:
Spoon a loose layer of biscuit crumbs into six glasses. Add a layer of cream, then repeat, finishing with cream and the reserved crumbs. Keep the layers slightly uneven rather than pressing them flat.
Cover and chill for at least 4 hours, or overnight, before serving cold.
Notes
Stop whipping when the mixture holds soft folds; overwhipped cream can turn grainy.
Keep covered and refrigerated for up to three days.