Bring a large pot of salted water to a rolling boil over high heat. Add macaroni and cook until al dente, approximately 7-9 minutes. Drain and set aside.

In a large saucepan over medium heat, melt the butter until foaming. Gradually whisk in the flour and cook for 2-3 minutes until golden and smooth.

Slowly pour in milk and heavy cream, whisking continuously for 5-7 minutes until thickened and bubbling gently.

Reduce heat to low and stir in cheddar and Monterey Jack cheeses until melted and smooth. Season with salt and pepper to taste.

Fold cooked macaroni into the cheese sauce, stirring for about a minute to ensure every piece is coated.

Serve immediately or transfer to a greased baking dish, sprinkle with breadcrumbs and extra cheese, and bake at 375°F for 20-25 minutes until golden.