Cook macaroni according to package directions. Drain the macaroni and place it in a greased 9x13 baking pan.
In a medium saucepan, melt 4 tablespoons butter. Add in the flour, salt and sugar, then stir until smooth.
Gradually add in the milk, stirring constantly. Bring to a boil; cook and stir for 2 minutes or until the mixture has thickened. Reduce the heat to low.
Stir in the Velveeta cheese until melted.
Stir in cottage cheese, sour cream and 1 cup cheddar cheese until melted.
Pour the cheese mixture over macaroni. Sprinkle with the remaining cheddar cheese.
Melt remaining butter and toss with bread crumbs; sprinkle over top the casserole.
Bake, uncovered, at 350° for 30 minutes or until golden brown.