1) To make the caramel sauce: Combine all of the sauce ingredients in a heavy-bottomed saucepan set over low heat. Stir at regular intervals until the caramel has melted and the mixture is smooth.
2) Bring the sauce just to a boil, then remove from the heat.
3) To make the apple bowls, cut off the top portion of the apples, and hollow out the cores and surrounding flesh with a melon baller, spoon, or whatever other tool you have handy.
4) Brush the lemon juice all over the inside of each apple.
5) Fill each apple with 1/2 cup of vanilla ice cream, drizzle with caramel sauce, and top with toasted nuts, if desired.
Yield: 4 sundaes.