Preheat oven to 425 degrees. Cook macaroni according to package directions. Drain and run under cold water. Melt butter over medium heat in a large saucepan. Whisk in flour, and let cook 2 minutes while stirring. Slowly whisk in cream, milk, mustard powder, and onion powder. Cook over medium heat while stirring until thickened. Remove from heat and stir in Parmesan cheese and 3 cups cheddar cheese until melted. Add soup if using. Toss cheese sauce and macaroni noodles together. Pour into a greased 9 x 13 inch pan. Top with remaining cheese. Bake 18-24 minutes or until bubbly. Do not over cook. Cool 10-15 minutes before serving.
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