Preheat oven to 425°F.
Cook macaroni al dente (firm) 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 milk, cream, mustard powder, onion powder, salt & pepper to taste. Cook over medium heat while stirring until thickened.
Remove from heat and stir in parmesan cheese & 3 cups cheddar cheese until melted. Add soup if using.
Toss cheese sauce & macaroni noodles together. Pour into a greased 9×13 pan. Top with remaining cheese.
Bake 18-24 minutes or until bubbly. Do not over cook. Cool 10-15 minutes before serving.
