Creamy Chicken Fettuccine Alfredo

Melt 2 tablespoons butter in a large skillet over medium heat. Add chicken, 1/2 of the garlic, and Italian seasoning. Cook until chicken is no longer pink in the center and the juices run clear. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Remove from the skillet and set aside.

Fill a large pot with lightly salted water and bring to a rolling boil. Cook fettuccine at a boil until tender yet firm to the bite, 8 to 10 minutes. Drain.

Meanwhile, melt remaining 4 tablespoons butter in the skillet. Add onion, mushrooms, and remaining garlic; sauté until onion is transparent, about 5 minutes. Stir in flour, salt, and pepper; cook for 2 minutes. Slowly add milk and half-and-half; cook and stir until smooth and creamy. Stir in both cheeses until melted.

Stir in chicken mixture, tomatoes, and sour cream. Serve over cooked fettuccini.