In a large bowl, combine flour, baking powder, and cinnamon; mix well. Stir in rolled oats and brown sugar.
In a medium bowl, beat butter, milk, sour cream and eggs until well blended. Add to dry ingredients; mix just until dry ingredients are moistened. Stir in apples and cranberries. Fill buttered muffin cups ¾ full. Sprinkle sugar evenly over muffins.
Bake at 425° F for 15 to 20 minutes or until light golden brown.