Cook macaroni according to package directions; drain. In a small skillet melt butter; add onion, salt, and garlic powder. Cook until onion is transparent. Cut 4 Frankfurter into 1-inch pieces, reserving 1 frankfurter for garnish. Combine macaroni, onion mixture, Frankfurter, cottage cheese and sour cream in casserole. Toss lightly until well mixed. Cut extra frankfurter crosswise into thin slices; arrange in a circle on the top casserole. Spread Cheddar cheese inside the ring of frankfurter slices; bake 30 minutes.