Bring a large pot of salted water to a rolling boil. Add elbow macaroni and cook until al dente, about 6-8 minutes. Drain and rinse with cold water.

In a medium saucepan over medium heat, melt 4 tablespoons of butter until bubbling. Whisk in 1/4 cup of flour and cook for about 2 minutes to form a roux.

Gradually pour in 3 cups of full-fat milk, whisking until the mixture thickens, about 5-7 minutes.

Remove from heat and stir in 2 cups of shredded cheddar cheese and 1 cup of grated Parmesan cheese until melted. Season with salt and pepper.

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

Transfer the mixture into a greased casserole dish, smoothing the top.

Cut mozzarella into ghost shapes and arrange on top of the pasta. Add sesame seeds or peppercorns for eyes.

Preheat oven to 375°F (190°C) and bake for 20-25 minutes until bubbly and golden brown.

Allow to cool for a few minutes before serving with mozzarella ghosts.