Pour the olive oil in a large, heavy bottomed pot over high heat. Season the meat with salt and pepper, then add to the pot in a single layer, working in batches if necessary. Allow the meat to brown really well on all sides, about 15 minutes, then remove from the pan.
Lower the heat to medium, then add the butter, onion and carrots. Sauté for about 5 minutes, then add the garlic and cook for one minute more. Add the tomato paste and stir until the vegetables are coated. Continue cooking and stirring for about 5 minutes, then add the potatoes and cook for 2 minutes more.
Add 1 teaspoon of thyme, the bay leaf, Guinness, beef broth, Worcestershire, sugar, and browned meat. Bring up to a boil, then lower the heat all the way and simmer until the stew has thickened slightly and the meat is falling apart, about 2-3 hours.
Taste and adjust the seasoning as needed. Stir in the remaining 1 teaspoon of thyme and half of the parsley.
Ladle the stew into bowls and garnish with a sprinkling of parsley. Serve hot.