Hoosier Apple-Yogurt Coffee Cake
["2/3 c. sugar", "1/2 c. butter or margarine", "2 eggs", "1 tsp. vanilla", "1 1/2 c. ground rolled oats*", "1 c. all-purpose flour", "1 tsp. baking powder", "1 tsp. baking soda", "1 (8 oz.) carton plain yogurt", "2 c. finely chopped, peeled cooking apples", "1/2 c. chopped nuts", "1/2 c. packed brown sugar", "1 Tbsp. butter or margarine, melted"]
["*Start with 1 2/3 cups oats; grind in blender or food processor."]
["sugar", "butter", "eggs", "vanilla", "ground rolled oats", "flour", "baking powder", "baking soda", "yogurt", "apples", "nuts", "brown sugar", "butter"]