Preheat oven to 350°F (175°C).

Cook macaroni according to package directions until al dente. Avoid overcooking.

Drain pasta thoroughly in a strainer.

Transfer the drained macaroni to a large, deep casserole dish.

Add butter to the macaroni and stir until melted and coated.

Season with salt and pepper, tasting and adjusting as needed.

Add mozzarella and 3 cups of cheddar cheese, reserving 1 cup of cheddar for topping.

In a separate bowl, whisk eggs until well combined.

Pour the whisked eggs over the macaroni mixture.

Stir gently with a large wooden spoon to evenly distribute the eggs and cheese.

Cover the casserole dish tightly with aluminum foil.

Bake in the preheated oven for 45 minutes.

Remove the foil and sprinkle the remaining 1 cup of cheddar cheese evenly over the top.

Return to the oven and bake uncovered for an additional 15-30 minutes, or until the cheese is melted, bubbly, and golden brown.

Let stand for a few minutes before serving.