Increase the oven's temperature to 350 degrees
Boil all the spaghetti in salted water until al dente. It'll keep baking. Drain and set aside pasta
Melt butter in a big pot and sauté minced garlic for 4-5 minutes on medium heat
Add salt, pepper, and nutmeg after a few minutes
Simmer the mixture with vinegar to reduce it further
Milk, flour, and chicken broth. Stir to thicken
Mix pasta, chicken thighs, mushroom mixture, and bacon
Place everything in a large baking dish and top with shredded cheese
Bake Chicken Tetrazzini at 350 degrees for 20–25 minutes until it bubbles and the cheese melts
Prepare it hot and garnish with chopped parsley