Grease a 11" by 7" or 2 quart square baking pan. Arrange apple slices in bottom of dish. Sprinkle with lemon juice, cinnamon, and nutmeg.
In a large bowl combine flour, the 2 tablespoons melted butter, brown sugar, milk, and vanilla. Stir in walnuts. Spread the batter evenly over the apples.
In a small saucepan combine the caramel topping, water, and the one tablespoon of butter. Bring to boiling. Pour over batter. Bake in a 350 degree oven for 35 minutes. While warm, spoon cake, apples, and caramel mixture into bowls. Serve with Vanilla Ice Cream.