Using a sharp knife cut across the grain of the beef brisket and dry the cubes with a paper towel. Season well with salt. Heat the oil in the Dutch oven and sear the beef on all sides until all the pieces are a very deep golden brown. You may need to brown the beef in batches. *see notes so that it doesn't steam due to an overcrowded pot. 

Once all the beef has browned remove it to a plate or bowl and add in the diced onion, garlic, celery, carrots, thyme and rosemary. As the onions sweat, they will release moisture. Use that to help scrape all the golden brown bits of beef on the bottom of the pan.

Stir in the flour and tomato puree. This helps to cook out the raw flour and mellow out the tomato flavour. These also help to thicken the liquid. Add the beef back to the pan. 

Deglaze the pan by pouring in the ale, beef stock and bay leaf. Give the bottom of the pan another scrape with a wooden spoon and bring everything to a high simmer and turn the heat down. Cover the stew with the pot lid and let gently simmer for about 4 hours until the beef is falling apart and the stew is thick.