Peel and slice apples. Put in a saucepan with 1/4 c. water; simmer for 2 to 3 minutes. While still on burner on low to medium, add brown sugar, cinnamon, nutmeg and 1/4 cup butter. Add cornstarch if necessary to make it a consistency of pie filling. Place in 9 inch square pan. In a separate bowl, mix cake mix, 1/2 stick butter and black walnuts. Sprinkle over apple mixture. Bake at 400 degrees for 20 to 30 minutes or until top is golden brown.