Start by bringing a large pot of salted water to a boil over high heat. Add the elbow macaroni and cook according to package instructions until al dente, usually around 8-10 minutes. Drain and set aside.

In a medium saucepan, melt 4 tablespoons of butter over medium heat. Sprinkle in 4 tablespoons of all-purpose flour, stirring continuously until it forms a pale roux, about 1-2 minutes.

Slowly whisk in 2 cups of milk while stirring constantly to avoid lumps. Cook until thickened and smooth, about 3-5 minutes.

Remove from heat and stir in 1 cup of sharp cheddar cheese and 1 cup of Monterey Jack cheese until melted and creamy.

Add the drained macaroni to the cheese sauce, mixing until thoroughly coated. If too thick, add pasta water to thin it out.

Transfer to a greased baking dish, sprinkle additional cheddar on top, and broil for 3-5 minutes until bubbly and golden brown.

Let the mac and cheese rest for 2-3 minutes before serving.