1. Cook pasta according to package directions; drain.
2. While pasta cooks, melt butter in a medium saucepan over medium heat. Add garlic, and cook, stirring often, until fragrant, about 1 minute. Add flour, and cook, stirring constantly, 1 minute. Gradually whisk in milk and cream; bring to a simmer, and cook, stirring often, until thickened, about 10 minutes. Remove from heat; whisk in cheeses, ½ teaspoon of the salt and ¼ teaspoon of the pepper. Cover and keep warm.
3. Sprinkle chicken with remaining 1 teaspoon salt and ½ teaspoon pepper. Heat a grill pan over medium high; lightly coat with cooking spray. Add chicken, and cook through, about 6 minutes per side. Remove from heat, and let rest 5 minutes before slicing.
4. Divide pasta among serving bowls; top with chicken slices and Alfredo sauce.
1 (1-lb.) pkg. fettuccine
6 tbsp. unsalted butter
1 tbsp. chopped garlic
2 tbsp. all-purpose flour
1 ½ cups whole milk
1 ½ cups heavy cream
2 oz. Parmesan cheese, grated (about ½ cup)
2 oz. Romano cheese, grated (about ½ cup)
1 ½ tsp. kosher salt, divided
¾ tsp. black pepper, divided
2 lbs. boneless, skinless chicken breasts