1. Heat olive oil in a large skillet over medium-high heat.
2. Add ground beef and cook until browned. Drain excess grease.
3. Stir in chopped onion, sliced mushrooms (if using), and minced garlic. Cook until the onion softens.
4. Add Worcestershire sauce, Dijon mustard, dried thyme, salt, and pepper.
5. Pour in beef broth and heavy cream (or cream of mushroom soup), stirring to combine.
6. Bring the mixture to a simmer and add cheese tortellini.
7. Cook for 3-9 minutes, depending on the tortellini type, until tender and the sauce thickens.
8. Remove from heat and stir in sour cream until smooth.
9. Garnish with fresh parsley and Parmesan cheese if desired. Serve immediately.