In a mixing bowl combine 2 1/2 cups flour, oats, sugar, and cinnamon. Beat in butter just until moistened. Set aside 2 cups for topping.
Pat remaining oat mixture into a greased 13-x-9-x-2-inch baking pan. Bake at 375° for 15 minutes.
Meanwhile, toss apples with remaining flour. Stir in preserves; spread over hot crust to within 1/2 inch of edge. Combine nuts and reserved oat mixture; sprinkle over fruit mixture. Bake 30 minutes longer or until lightly browned. Cool completely before cutting.
Yield: Four dozen bars.