Add chicken broth slowly, whisking continuously until the garlic mixture is smooth. Add milk and bring the mixture to a simmer. Cook for an additional minute until thickened, then stir in Parmesan cheese, salt and pepper until the cheese is fully melted. Reduce heat to medium-low and add pasta to the pan. Turn the heat off and toss until the pasta and sauce are combined, then stir in chicken breasts and broccoli.
Toss until sauce coats pasta, chicken and vegetables. Add a little reserved pasta cooking water if sauce is too thick. Serve immediately, topped with chopped pasta if needed.
Recipe by In Good Taste at http://ingoodtaste.kitchen/skinny-chicken-broccoli-alfredo/