Fill your biggest pot with water and add a generous pinch of salt. Bring to a rolling boil over high heat. Add fettuccine and stir to prevent sticking. Cook for about 10 minutes until al dente (tender but with a slight bite). Before draining, scoop out half a cup of pasta water. Drain pasta and set aside.
Pat chicken breasts dry with paper towels. Sprinkle both sides evenly with Italian seasoning, 3/4 teaspoon salt, and 1/4 teaspoon pepper.
Heat olive oil in a large nonstick skillet over medium-high heat until shimmering. Add chicken and don't touch it for 5-7 minutes until the bottom is beautifully browned.
Flip chicken over and drop 1 tablespoon butter between the pieces. Gently swirl the pan. Continue cooking for another 5-7 minutes until internal temperature reaches 165°F.
Transfer chicken to a cutting board and let rest for 3 minutes. Slice into half-inch pieces and tent loosely with foil to keep warm.
Lower heat to medium-low. Add 1/2 cup butter and heavy cream to the same pan (don't wash it). Whisk gently until butter melts completely.
Add minced garlic, garlic powder, remaining Italian seasoning, salt, and pepper. Whisk until everything combines into a smooth mixture.
Bring sauce to a gentle simmer with tiny bubbles around the edges. Whisk constantly for 3-4 minutes as it thickens until it coats the whisk beautifully.
Remove pan from heat. Add freshly grated parmesan gradually, stirring until it melts into silky perfection. If sauce is too thick, add reserved pasta water one tablespoon at a time.
Add cooked fettuccine directly to the pan. Using tongs, toss everything together until every strand is coated in sauce.
Divide pasta among serving bowls and top each portion with sliced chicken. Garnish with extra parmesan, freshly cracked black pepper, and fresh parsley if desired.