To the pan that you seared the beef short ribs, add reserved celery, garlic, and leeks in the same pot used to sear the beef short ribs. Stir to mix.
Once the leeks, garlic, and celery become soft, add a large pinch (1 tsp) of the seasoning flour along with the thyme and bay leaves. The addition of flour will help set up the sauce later. Stir to mix in and cook for two minutes.
Deglaze with the Guinness Draught beer. Cook and bring to a boil.
Add the balsamic vinegar, beef stock, tomato sauce, tomato paste, thyme, bay leaf, and soy sauce. Stir to incorporate.
Add the seared beef short ribs back on top of the vegetable/beer mixture, along with any accumulated juices. Bring to a simmer.
Add the reserved carrot and boiler onions around the meat. Cover the pot with a tight-fitting lid and place it into a pre-heated oven at (350°F or 175°C) for 2 hrs 20 minutes. (Alternatively, cover with foil if no top is available.)
Test the beef short ribs for doneness with the tip of a knife. The blade should easily pierce and come out of the beef. The beef should be super soft but not yet falling apart.
After the meat is cooked, carefully remove the short ribs by lifting them out with a combination of a long sturdy metal spatula and a set of tongs. Place the meat on a clean plate and reserve.