Soak the gelatine in the cold water. Heat milk, maple syrup and salt in the top if a double boiler, then slowly add the egg yolks. Add the gelatine, stir to dissolve and let the mixture cool.
Whip the cream, flavor it with vanilla and set half of it aside. Fold the rest, along with the egg whites, into the cooled custard. Pour into the baked pie shell, top with remaining whipped cream and refrigerate until well chilled.