1. 1. In a large bowl, combine the ground beef, breadcrumbs, milk, egg, garlic powder, onion powder, dried parsley, salt, and pepper. Mix well until fully incorporated.

2. 2. Roll the mixture into 1-inch meatballs.

3. 3. In a large skillet, heat the olive oil over medium-high heat. Add the meatballs and cook, turning occasionally, until browned on all sides, about 5-7 minutes. Transfer the meatballs to a plate.

4. 4. In the same skillet, sauté the onion until translucent, about 3-4 minutes. Add the garlic and cook for 1 minute more.

5. 5. Pour in the Guinness beer and beef broth. Stir in the Worcestershire sauce and Dijon mustard. Bring the mixture to a simmer.

6. 6. In a small bowl, whisk together the cornstarch and water to make a slurry. Slowly pour the slurry into the simmering gravy, whisking continuously, until the gravy thickens, about 2-3 minutes.

7. 7. Reduce the heat to low, add the meatballs back to the skillet, and simmer for 10-15 minutes, or until the meatballs are cooked through.

8. 8. Garnish with fresh parsley and serve immediately.