Heat the vegetable oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Season the beef cubes generously with salt and pepper, then sear them in batches until browned on all sides, about 5-7 minutes per batch.

Remove the beef and set aside. Add the chopped onion, sliced carrots, and celery to the pot, sautéing for about 5 minutes until they begin to soften and release their aroma.

Return the beef to the pot and pour in the beef broth and Worcestershire sauce. Stir in the dried thyme, scraping up any browned bits from the bottom of the pot to enhance the flavor.

Bring the mixture to a boil, then reduce the heat to low. Cover the pot and let it simmer gently for 1.5 hours, or until the beef is fork-tender.

While the stew simmers, prepare the dumplings by whisking together the flour, baking powder, 1/2 tsp salt, and chopped parsley in a medium bowl. Cut in the cold grated butter until the mixture looks like coarse crumbs, then stir in the milk until a soft dough forms.

Stir the frozen peas into the stew and adjust the seasoning with more salt and pepper if desired.

Drop heaping tablespoons of the dumpling dough directly onto the surface of the simmering stew, spacing them out slightly. Cover the pot tightly with a lid and simmer for 15-20 minutes without lifting the lid to allow the dumplings to steam properly.

Once the dumplings are fluffy and cooked through, remove from heat. Serve immediately, ladling the thick gravy, vegetables, and beef over the warm dumplings.