Grease a 9×13-inch pan. Preheat oven to 375°F (190°C).
Boil pasta in salted water until al dente. Drain and return to pot.
Combine both cheddar cheeses. Set aside half for topping.
Melt butter, whisk in flour, and cook 1–2 mins. Slowly add milk; stir until thickened. Remove from heat, season, and stir in half the cheese until smooth.
Mix pasta with cheese sauce.
Layer half the mac in the dish, add one-third of reserved cheese, then repeat with remaining pasta and top with rest of cheese.
Bake uncovered for 15–20 mins until bubbly and golden.