Preheat oven to 350°.
To prepare cake, beat sugar, oil, and eggs at medium speed of a mixer until well-blended. Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (flour through nutmeg) in a small bowl. Add flour mixture to sugar mixture, beating just until blended. Fold in apple and walnuts.
Pour batter into a 13 x 9-inch baking pan coated with cooking spray. Bake at 350° for 55 minutes or until a wooden pick inserted in center comes out clean. Run a knife around outside edge; cool.
To prepare sauce, combine raisins and rum in a microwave-safe bowl; let stand 5 minutes. Stir in butterscotch topping; microwave on high 45 seconds or until hot. Serve cake with sauce.
Note: Cake will keep for several days in an airtight container, but the crunchy top will soften.