Heat 1 tsp of olive oil in a Dutch oven over medium heat. Add the beef and onions; cook for 5 minutes.
Add the garlic and cook for 30 seconds or until fragrant. Add the beef stock, diced tomatoes, bay leaves, thyme and rosemary. Season to taste with salt and pepper, then cover and cook in a 250-degree oven for 4-5 hours.
Remove the pot from the oven and place over medium-low heat. Add the carrots, celery and potatoes, topping off with more beef stock if needed.
Cover and cook for 1 to 1 1/2 hours. Whisk together the cornstarch and cold water or stock; bring the stew to boiling, then slowly stir in the cornstarch slurry. Reduce the heat to low and cook until thickened, about 5 minutes.
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