Cook macaroni and drain. Once drained, place in a 2½ quart dish.
In a large saucepan, melt 4 tbsp butter. Stir in flour, salt, and sugar until smooth. Gradually stir in the milk. Bring to boil, cook and stir 2 minutes until thickened. Reduce heat and stir in cubed cheese until melted. Next stir in cottage cheese and sour cream.
Pour over macaroni and sprinkle with sharp cheese.
Melt remaining butter and toss with bread crumbs. Sprinkle over the top of macaroni and cheese mixture.
Bake at 350 uncovered for 30 minutes or until brown.