Boil the cubed potatoes in salted water for 15 to 18 minutes until fork-tender. Drain and set aside.
Mix ground beef, breadcrumbs, egg, 1 tsp Worcestershire, garlic powder, onion powder, salt, and pepper. Roll into 1.5-inch meatballs.
Heat olive oil in a large skillet over medium-high. Sear meatballs 2 to 3 minutes per side until browned. Remove and set aside.
Melt butter in the same skillet. Add onion and mushrooms, cook 4 to 5 minutes. Add minced garlic and cook 30 seconds more.
Sprinkle flour over vegetables and stir. Slowly pour in beef broth while stirring, then add remaining Worcestershire and Dijon mustard. Simmer 3 minutes until slightly thickened.
Return meatballs to the skillet. Cover and simmer on low for 8 to 10 minutes until cooked through.
Mash drained potatoes with butter, warm cream, sautéed garlic, fresh herbs, and salt until smooth and creamy.
Serve meatballs and gravy over a generous scoop of garlic herb mashed potatoes.