Heat vegetable oil in a large Dutch Oven or pot over medium-high heat. Add diced bacon and cook for 4-5 minutes until crispy. Remove with a slotted spoon and reserve.

Season the beef generously with salt and pepper. Brown the beef in batches, ensuring not to overcrowd the pot, about 1-2 minutes per side. Remove and reserve with the bacon.

Lower the heat to medium. If necessary, add more oil, then stir in the onions and cook until browned, about 5 minutes. Add garlic and cook until fragrant.

Stir in the flour and tomato paste. Cook for 1-2 minutes until the paste darkens. Add the Guinness beer and scrape up any browned bits from the bottom of the pot with a wooden spoon.

Add the beef broth, brown sugar, Worcestershire sauce, salt, and pepper. Stir in the browned beef and bacon along with the thyme sprigs. Bring to a boil.

Once boiling, cover and reduce the heat to a simmer. Cook for 1 hour.

Add carrots and potatoes, cover, and continue cooking for another hour or until the beef is tender and the vegetables are cooked.

If the stew is not thickened to your liking, increase the heat to medium-high and boil uncovered until thickened. Optionally, add a slurry of equal parts flour and cold liquid (beer, broth, or water) to thicken further.

Discard the thyme sprigs, adjust seasoning if needed, and stir in the chopped parsley. Serve hot.