In a large bowl, mix together the ground beef, garlic powder, onion powder, salt, Italian seasoning, pepper, egg, bread crumbs, Worcestershire sauce and whole milk until fully combined.
Form golf ball-sized meatballs—about 2 tablespoons each—and place them on a plate, about 24 total.
Heat 2 tablespoons of olive oil in a large Dutch oven or heavy-bottom stock pot over medium high heat. Brown the meatballs on all sides but don’t worry about cooking them through.
Deglaze the pan with a few tablespoons of beef stock if necessary. To the same pot add the remaining tablespoon olive oil along with the onions, celery and carrots. Cook until vegetables are beginning to soften, about 5 minutes.
Add in the tomato paste and thyme, stirring to combine. Add the meatballs back to the pot along with the beef stock and the beef bouillon. Bring to a boil then reduce to a simmer.
Add in potatoes and green beans, cover with a tight fitting lid and simmer for 20 minutes until the vegetables are tender and meatballs register 160°F.
In a small bowl, mix the cornstarch and water together until smooth. Add the cornstarch slurry to the stew broth and stir over low heat until stew has thickened, about 5-7 more minutes.
Serve the stew sprinkled with parsley with some good crusty bread or buttered egg noodles.