Line a lightly buttered loaf pan with parchment paper, and place it in the freezer. Add two teaspoons pure vanilla to 14-ozs. sweetened condensed milk and refrigerate. Whip two cups of heavy cream to stiff peaks. Working quickly, GENTLY fold the whipped cream into the sweetened condensed milk, along with any additions—mashed macerated fruit, chocolate syrup, or crushed cookies or nuts—until well blended. Pour into the cold loaf pan and cover with plastic wrap. Freeze for at least four hours. Some recipes will tell you to stir the mixture after about two hours (while you still can) but you don’t have to.
