Cook the Pasta:

Bring a large pot of salted water to a boil. Cook the pasta according to the package instructions until al dente. Drain and set aside.

Make the Roux:

In a large saucepan or skillet over medium heat, melt the butter. Once melted, whisk in the flour and cook for 1-2 minutes, stirring constantly, until the mixture is golden and smooth (this removes the raw flour taste).

Add Milk and Cream:

Slowly pour in the milk and heavy cream while whisking continuously to prevent lumps. Cook for 3-4 minutes until the sauce begins to thicken.

Flavor the Sauce:

Stir in the Dijon mustard, salt, and black pepper.

Add the Cheese:

Reduce the heat to low and gradually add the shredded white cheddar cheese and cubed American cheese (if using), stirring until melted and creamy.

Combine with Pasta:

Add the cooked pasta to the cheese sauce and stir until the pasta is evenly coated.

Serve:

Serve warm with an optional sprinkle of extra shredded cheese on top.