In a large bowl: place beef, salt, pepper and mix.
Heat the dutch oven or pot to medium-high. Add oil and wait until hot. Place half of the beef in the dutch oven/pot and sear all sides for 3-5 minutes or until brown. Repeat this step with the other half of beef.
Placed seared beef in the slow cooker. Add tomato paste, rosemary, Worcestershire sauce, garlic, onion and mix. Add carrots, potatoes, celery, beef broth, bay leaves and thyme stems.
Cover and cook on low for 7-8 hours.
Discard thyme & bay leaves. In a bowl: add flour and 1 cup of the liquid from the beef stew. Whisk until smooth and pour in the slow cooker.
Cover and cook on high for 30 minutes. Season with salt and pepper to taste.