In a large pot over medium high, heat the vegetable oil until shimmering. Toss in the chunks of beef and cook until just browned on the outsides, about 2-3 minutes. Remove from the pot and set aside.
Add the chopped potatoes, stirring occasionally, until they begin to lightly brown. Then add the onions and cook until softened, about 4-5 minutes.
Add the carrots and celery to the pot. Cook until the celery brightens in color, about 1-2 minutes, then add the garlic, salt and pepper. Sprinkle the flour across the vegetables and stir until everything is coated in flour.
Pour the chicken, beef, and garlic broth (if using) into the pot and bring to a rolling boil. Reduce the heat to a simmer, cover, and let stew about 20-25 minutes.
While the stew cooks, start making the dumplings. Whisk together the flour, salt, pepper, baking powder and the herbs. In a separate bowl, stir together the milk and egg.
Roughly chop the chilled butter into small pieces (or use a food processor). Add the butter to the dry mix and stir until the mixture is crumbly - rub larger pieces of butter between your fingers, as needed, to achieve this.
Slowly pour the milk mix into the dry mix. Stir together until a thick batter-like dough forms. You should be able to pull off individual pieces without it sticking to your fingers. Pull off 1-2 tablespoon sized chunks of dough and roll between your palms to create a dough ball. Let the dough rest for about five minutes.
When the stew has about ten minutes remaining, return the meat to the stew then begin adding the dough balls to the pot. The dough should form an even layer on the top of the stew.
Cover the pot and let cook for about 10-15 minutes, until the dough is cooked though and puffed up. Serve the stew to S.P.E.W. supporters, friendly wizards and of course, the boy who lived. Enjoy!