Heat oven to 350°F. Grease bottom and sides of 8-inch square pan with shortening.
In large bowl, mix brown sugar and softened butter with spoon until light and fluffy. Beat in egg. Stir in flour, baking soda, 1 teaspoon cinnamon, the nutmeg and salt. Stir in apples. Spread batter in pan.
Bake 25 to 35 minutes or until toothpick inserted in center comes out clean.
Meanwhile, in 1-quart saucepan, heat sauce ingredients over medium heat, stirring frequently, until butter is melted and sauce is hot. Serve warm sauce over warm cake.