Preheat your oven to 350°F (180°C). Butter a 9×13-inch baking dish.
Bring a large pot of salted water to a boil. Add the macaroni and cook according to the package instructions until al dente. Drain the macaroni and set it aside.
In a large saucepan, melt the butter over medium heat. Add the flour and whisk together until the mixture forms a paste.
Gradually add the milk, whisking constantly, until the mixture is smooth. Bring the mixture to a simmer, whisking frequently, until it thickens and coats the back of a spoon.
Remove the saucepan from the heat and stir in the cheddar cheese, Monterey Jack cheese, Dijon mustard, salt, pepper, and cayenne pepper until the cheese is melted and the sauce is smooth.
Add the cooked macaroni to the cheese sauce and stir until the macaroni is evenly coated.
Pour the macaroni and cheese into the prepared baking dish and smooth the top with a spat
