Creamy Beef and Noodles

Name: Creamy Beef and Noodles
Ingredients: 1 (12-ounce) package frozen homestyle egg noodles, such as Reames; 1/2 large yellow onion; 1 pound boneless beef sirloin steak; 1 teaspoon kosher salt, plus more as needed; 1/2 teaspoon freshly ground black pepper, plus more as needed; 3 tablespoons olive oil, divided; 1 (8-ounce) package sliced baby bella or cremini mushrooms; 4 sprigs fresh thyme; 1 tablespoon all-purpose flour; 3/4 cup beef broth; 1/4 cup dry red wine; 1 cup sour cream; 1 tablespoon Dijon mustard; 1 tablespoon chopped fresh parsley leaves (optional)