Bring a large pot of salted water to a boil, add macaroni, and cook until al dente, about 7-9 minutes. Drain and set aside.

In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 2 minutes to form a roux.

Gradually pour in milk while whisking, cooking until thickened, about 5-7 minutes.

Remove from heat, stir in cheddar and Parmesan cheese until melted and smooth. Season with salt and pepper.

Fold the cooked pasta into the cheese sauce until well-coated.

Preheat oven to 375°F (190°C) and transfer pasta mixture to a buttered casserole dish.

Cut mozzarella into ghost shapes and place on top of the pasta, adding sesame seeds for eyes.

Bake for 20-25 minutes until bubbly and golden brown. Let cool slightly before serving.