Bring a large pot of salted water to a boil. Cook fettuccine according to package directions until al dente. Reserve 1 cup pasta water, then drain and toss pasta with a splash of oil.

Cut chicken breasts in half lengthwise to make 6 thin cutlets. Combine Italian seasoning, salt, pepper, garlic powder, and paprika. Season both sides of chicken.

Heat olive oil and 3 Tbsp butter in a large nonstick skillet over medium-high heat. Add chicken and cook undisturbed for 4-6 minutes per side until golden and internal temperature reaches 165F. Remove to a plate, tent with foil, and slice into strips.

Reduce heat to medium and add remaining 9 Tbsp butter to the same skillet. Add minced garlic, garlic powder, nutmeg, salt, and pepper. Cook 1 minute, stirring constantly and scraping up browned bits.

Whisk in heavy cream and bring to a gentle simmer. Let bubble for 2 minutes to thicken slightly, then reduce heat to low.

Remove pan from heat and whisk in Parmigiano-Reggiano in handfuls until melted. Add reserved pasta water if sauce is too thick.

Add cooked fettuccine to sauce and toss well with tongs. Adjust seasoning to taste.

Divide pasta among bowls and top with sliced chicken. Garnish with fresh parsley and extra Parmigiano-Reggiano.