Bring a large pot of salted water to a boil.

Once boiling, add the elbow macaroni and cook until al dente, about 8 minutes.

Drain the pasta in a colander and set aside.

In the same pot, melt the unsalted butter over medium heat.

Whisk in the all-purpose flour and cook for about 1 minute, stirring constantly.

Slowly add the milk while whisking to prevent lumps.

Cook the sauce, stirring regularly, until it thickens and bubbles, about 5 minutes.

Stir in the shredded sharp cheddar cheese and shredded Monterey Jack cheese until melted and smooth.

Fold the cooked macaroni into the cheese sauce until well coated.