Melt butter in a large skillet over medium heat. Add mushrooms, onion and garlic to the skillet and sauté until tender (about 8-9 minutes). Remove from skillet and set aside on a plate.
Next, brown the ground beef in the same skillet until no longer pink (about 7 minutes). If you’re not using extra lean ground beef, you may need to drain off some of the fat at this point. Add thyme, rosemary, 1 cup of the broth, salt and Worcestershire sauce. Bring to a boil, and then reduce heat to low. Cover and simmer over low heat for about 10 minutes.
In a small bowl, whisk together remaining ½ cup of broth with the flour. Stir into beef mixture. Add onion mixture back to the skillet and bring to a boil, stirring constantly. Boil and stir for 1 minute, and then reduce heat to low. Stir in the sour cream and keep over low heat, just until warmed through (do not boil). Taste and season with additional salt and pepper, if necessary.
Serve over cooked noodles or rice and garnish with fresh parsley, if desired.