Heat olive oil in a large skillet over medium-high heat.
Add beef cubes in batches and brown on all sides, about 5 minutes per batch. Transfer browned beef to the slow cooker.
In the same skillet, add chopped onion and cook for 3-4 minutes until softened.
Add minced garlic and cook for 1 minute until fragrant.
Transfer onion and garlic to the slow cooker.
Add sliced carrots, diced potatoes, and sliced celery to the slow cooker.
Pour in beef broth and red wine.
Stir in tomato paste, dried thyme, dried rosemary, and bay leaf.
Season with salt and black pepper to taste.
Cover and cook on low for 7 hours, or until beef is tender and vegetables are cooked through.
About 30 minutes before serving, mix all-purpose flour and cold water in a small bowl to create a slurry.
Stir slurry into the slow cooker to thicken the sauce.
Replace the lid and cook on high for 30 minutes until the sauce is thickened.
Remove bay leaf before serving.
Garnish with chopped fresh parsley and serve hot.