Fill a medium sized pot with water and bring to a boil, then add tortellini and cook according to package instructions. In the meantime, melt butter in a small sauce pan over medium heat and add the minced garlic. Sauté garlic for about a minute, then whisk in flour. Gradually whisk in milk, then both cheeses, salt, and pepper. Continue to cook, stirring frequently, until cheese melts and sauce is smooth. Drain cooked tortellini and stir in cheese sauce. Serve immediately, garnished with extra Parmesan if desired.