Pat the pork stew meat dry and season it with the salt and black pepper. Heat the vegetable oil in a large Dutch oven over medium-high heat, then brown the meat in batches until all sides are seared. Remove the meat and set it aside.

Lower the heat to medium and add the diced onion, carrots, and parsnips to the pot. Cook for 5 minutes, stirring occasionally, until the onion softens.

Stir in the minced garlic and cook for 1 minute more. Sprinkle the flour over the vegetables and stir for 2 minutes to coat everything and remove the raw flour taste.

Pour in the Guinness and scrape the bottom of the pot to release any browned bits. Let the liquid simmer for 2 minutes.

Return the browned pork to the pot along with the beef broth, thyme sprigs, and bay leaves. Bring the mixture to a boil, then reduce to a low simmer.

Cover the pot and cook for 1 hour and 15 minutes, stirring every 20 minutes. Add the potato cubes during the last 30 minutes of cooking so they become tender but not mushy.

Remove the thyme sprigs and bay leaves. Taste and adjust salt if needed. Sprinkle with the chopped parsley just before serving.