Chicken Fettuccini Alfredo

INGREDIENTS

• 6 skinless, boneless chicken breast halves - cut into cubes
• 6 tablespoons butter, divided
• 4 cloves garlic, minced, divided
• 1 tablespoon Italian seasoning
• 1 pound fettuccini pasta
• 1 onion, diced
• 1 (8 ounce) package sliced mushrooms
• 1/3 cup all-purpose flour
• 1 tablespoon salt
• 3/4 teaspoon ground white pepper
• 3 cups milk
• 1 cup half-and-half
• 3/4 cup grated Parmesan cheese
• 8 ounces shredded Colby-Monterey Jack cheese
• 3 roma (plum) tomatoes, diced
• 1/2 cup sour cream