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 until softened, about 3 minutes.
Add minced garlic and cook for 1 minute more.
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, then stir in tomato paste, dried thyme, dried rosemary, and bay leaf.
Season with salt and black pepper to taste and stir gently to combine all ingredients.
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 with cold water to make a slurry.
Stir the slurry into the slow cooker to thicken the sauce.
Cover and cook on high for an additional 30 minutes until the sauce has thickened.
Remove bay leaf before serving.
Garnish with chopped fresh parsley and serve hot.