01 - Boil pasta in a large pot of salted water according to package directions until al dente. Drain, reserving 120 milliliters (1/2 cup) of pasta water.
02 - Melt butter in a medium saucepan over medium heat. Whisk in flour and cook for 1 minute until lightly golden.
03 - Gradually whisk in the warmed milk, stirring continuously to achieve a smooth consistency. Simmer for 3–4 minutes until the sauce thickens.
04 - Remove from heat and incorporate Parmesan cheese, salt, pepper, and nutmeg. If the sauce is too dense, thin with reserved pasta water as needed.
05 - Toss the drained pasta with the velvety white sauce until thoroughly coated.
06 - Transfer the coated pasta to a serving platter or individual plates. Cut mozzarella into ghost shapes and arrange atop the warm pasta to partially melt.
07 - Place two black olive slices on each mozzarella ghost to form eyes. Garnish with fresh parsley, if desired.
08 - Serve the pasta immediately.