Begin by adding your stewing beef to a large bowl. Add your flour and toss to combine, ensuring all pieces have been fully covered.
To a large pan, add your vegetable oil and once hot, add your beef and brown on each side. Work in batches if you need, to avoid crowding the pan. This should only take 2-3 minutes, don't worry about cooking the beef all the way through.
Remove the beef using a slotted spoon and set aside.
To the same pan, reduce heat to low and add your wine. Scrap all the bits from the bottom of the pan and let simmer for 1-2 minutes then turn off the heat. Set aside while you prepare your other ingredients.
Chop your carrots, celery, onions, and potatoes into similar sized pieces, about 1/2 inch. Set aside.
To your crockpot, add your beef, red wine, carrots, celery, onions, potatoes, garlic, tomato sauce, beef stock, worcestershire, bay leaf, and thyme. Mix to combine.
Set your crockpot to low, and cook for 8-9 hours. Alternatively, you can set to high for 4-5 hours.
During the last 30-40 minutes of cook time, add your flour and butter to a small saucepan and cook on low, whisking continuously until you have created a smooth roux, this should take about 3-4 minutes. Add the roux to your crockpot, stir to combine, and let the stew cook for an additional 30 minutes. If the beef is still tough, cover the crockpot and continue cooking for another hour or until tender.Taste before serving in case you need any additional salt/pepper. Top with fresh parsley and serve along side homemade biscuits or mashed potatoes.