Preheat the oven to 300°F (150°C).
Season the beef cubes with salt and pepper.
Heat the olive oil in a large, oven-safe pot or Dutch oven over medium-high heat.
Add the beef to the pot and sear on all sides until browned, about 2-3 minutes per side.
Remove the beef from the pot and set aside.
In the same pot, sauté the onion and garlic until they are soft and translucent, about 5 minutes.
Stir in the tomato paste and cook for 1-2 minutes more.
Add the Guinness, beef broth, thyme, rosemary, and bay leaf to the pot and bring the mixture to a boil.
Return the beef to the pot and add the carrots, parsnips, and potatoes.
Cover the pot with a lid and transfer it to the oven.
Bake for 2-2.5 hours, or until the beef is tender and the vegetables are cooked through.
Garnish with chopped fresh parsley and serve hot with mashed potatoes or crusty bread.
