Heat olive oil in a large skillet over medium-high heat.
Add beef cubes in batches and brown on all sides, about 4-5 minutes per batch. Transfer browned beef to the slow cooker.
In the same skillet, add diced onion and cook for 3-4 minutes until softened.
Add minced garlic and sliced mushrooms to the skillet and cook for another 4-5 minutes until mushrooms release their moisture and begin to brown.
Transfer the onion, garlic, and mushroom mixture to the slow cooker with the beef.
Add beef broth, tomato paste, dried thyme, dried rosemary, bay leaf, Worcestershire sauce, salt, and black pepper to the slow cooker. Stir to combine.
Cover and cook on low for 6 hours or until the beef is tender.
About 15 minutes before serving, mix cornstarch and cold water in a small bowl until smooth.
Stir the cornstarch slurry into the slow cooker to thicken the sauce. Cover and cook on high for 15 minutes.
Remove the bay leaf and stir in chopped fresh parsley.
Serve hot over mashed potatoes, rice, or egg noodles.