Start by cooking the penne pasta until al dente in a pot of boiling salted water. Set aside ½ cup of cooking water. Drain and reserve.
Melt the butter over medium heat in a large skillet and saute the garlic for about 30 seconds.
Add the flour and cook it in the melted garlic butter for one minute.
Using a whisk, carefully mix in the chicken broth, milk, half of the parmesan cheese, red pepper flakes, parsley, salt and pepper.
Cook the sauce until slightly thick.
Mix in the cooked pasta. If you feel the sauce is too thick, add a bit of the reserved cooking water to thin it out.
Serve with additional parmesan cheese on top.