Beef: Cut the beef chuck into cubes, about 3 cm/ 1.2 inches. Place them on paper towels and pat them dry with more paper towels.
Flour beef: Place the flour in a large bowl, add some salt and pepper, and mix well. Add some of the beef cubes and toss to coat with the flour. Pat gently to remove the excess flour.
Brown beef: Heat about 1 tablespoon of the oil in a large heavy-bottomed pot over high heat. Add some beef cubes and brown all over; this will take about 5 minutes per batch. Remove onto a plate and repeat with the remaining beef (Note 2).
Vegetables: While the meat browns, chop the vegetables. Keep the onions separated from the rest. Set aside.
Cook vegetables: Add the remaining oil to the pot and lower the heat to medium. Add the onions and cook for about 3 minutes until softer. Stir often. Add the garlic, carrot, and celery and cook for another 5 minutes.
Add the sugar, tomato paste, and dried thyme, stir very well for about 1 minute. Pour in the Guinness and deglaze the bottom of the pot, scraping up the brown bits on the bottom.
Return the beef and its juices to the pot. Add the bay leaves and enough beef broth just to cover the meat.
Simmer: Bring to a boil, lower the heat, cover the pot and simmer for about 2 ½ hours or until the meat is really tender and almost falls apart.
Thicken: If the sauce is too thick after 2 ¼ hours, remove the lid and continue cooking the stew until the sauce has thickened as much as you like it.
Adjust the taste with salt and pepper.