Cook macaroni according to package directions then drain and place in a buttered 2 ½ qt. baking dish.
In a saucepan, melt 4 Tablespoons butter. Stir in the flour, salt & sugar until smooth. Gradually add the milk, and stir, bringing it to a boil, and continue to cook & stir, until thickened. Reduce the heat., and stir in the Velveeta until melted. Stir in the cottage cheese & sour cream and pour mixture evenly over the macaroni in dish.
Sprinkle with the Cheddar Cheese. Melt remaining 2 Tablespoons of butter & toss with the bread crumbs and sprinkle over the top.
Bake, uncovered at 350 degrees F for 30 min., or until golden brown.