Preheat oven to 350°. Cook noodles according to package directions; drain. In large skillet, saute onion and green pepper in butter 3 minutes or until tender. Add beef and cook until no longer pink. Drain excess fat. In medium bowl, combine tomato paste and sour cream; stir in noodles and cottage cheese. Layer half the noodle mixture in 2 quart casserole; top with half the beef mixture. Repeat. Pour tomato sauce evenly over top of casserole. Bake 30 to 35 minutes or until heated through.