Prepare tortellini according to the directions on the package.
In the meantime, heat olive oil in a large nonstick skillet over medium-high heat.
Add garlic and cook one minute, stirring occasionally, until fragrant.
Add flour and whisk to combine; continue to whisk and cook for an additional minute to cook the flour.
Slowly add broth, whisking to combine until smooth.
Whisk in milk and bring mixture to a boil.
Continue to cook for 1 to 2 minutes, or until thickened.
Stir in parmesan cheese, salt and pepper; continue to cook and stir until the cheese is completely melted.
Reduce heat to medium-low.
Drain tortellini and add them to the skillet with the sauce.
Stir to combine and continue to cook until heated through; about 1 minute.
Sprinkle with fresh rosemary or fresh chopped parsley and serve.