Cook macaroni according to package directions. Meanwhile, in a large saucepan, melt butter. Stir in flour until smooth. Gradually add milk. Being to a boil; cook and stir for 2 minutes or until thickened.

Reduce heat; stir in the sour cream, processed cheese, parmesan cheese, mustard, salt and pepper until smooth and cheese is melted.

Drain macaroni; toss with cheddar cheese. Transfer to a greased 3-qt baking dish. Stir in cream sauce.

Bakw, uncovered, at 350 for 35-40 minutes is until golden brown and bubbly.