Begin by bringing a large pot of salted water to a boil. Add elbow macaroni and cook according to package instructions until just al dente, usually about 7-8 minutes. Drain the pasta, ensuring to let it steam off for a minute, then set it aside.

In a medium saucepan over medium heat, melt the butter until it starts to bubble. Whisk in the flour and cook for about 2 minutes, stirring constantly to avoid browning, achieving a smooth roux.

Gradually whisk in the milk, continuing to stir until the mixture thickens, about 5 minutes. Once thickened, remove from heat and stir in the cheddar and Parmesan until fully melted and smooth.

With the cheese sauce still warm, season generously with salt and pepper and fold the cooked macaroni into the sauce, ensuring every piece is coated.

Preheat your oven to 375°F (190°C) and transfer the pasta into a buttered casserole dish, spreading it evenly.

Take slices of mozzarella and cut them into ghost shapes. Place these on top of the mac and cheese, spacing them out. Dot 'eyes' with sesame seeds or peppercorns.

Bake for 20-25 minutes until the top is bubbly and golden brown, ensuring the mozzarella ghosts are well melted but defined.

Allow to cool for a few minutes before serving in bowls, making sure each serving features a mozzarella ghost.