Place peeled and quartered potatoes in a pot of cold salted water. Bring to a boil and simmer until fork-tender, about 15–18 minutes. Drain and return to the pot.

In a large bowl, combine ground beef, breadcrumbs soaked in milk, egg, finely chopped onion, minced garlic, Worcestershire sauce, Dijon, salt, and pepper. Mix gently until just combined—overworking makes dense meatballs.

Form the mixture into golf-ball-sized meatballs.

Heat butter and oil in a large skillet over medium-high heat. Add meatballs in a single layer, leaving space between them. Brown on all sides until a crust forms and juices run clear, about 8–10 minutes. Remove and set aside.

Reduce heat to medium. If needed, add a touch more butter. Stir in flour and cook for 1 minute until it smells nutty. Whisk in beef broth and tomato paste, scraping the browned bits from the bottom. Simmer until slightly thickened, 3–4 minutes.

Return meatballs to the skillet and spoon gravy over them. Cover and simmer gently for 8–10 minutes so the meatballs finish cooking and soak up the sauce.

While the meatballs simmer, mash the drained potatoes with butter, warm milk or cream, and the soft roasted or sautéed garlic. Aim for a creamy but slightly rustic texture—leave a few lumps for heartiness.

Stir in chives and parsley, and season to taste.

Plate generous spoonfuls of garlic herb mashed potatoes, nestle 3–4 Salisbury steak meatballs on top, and ladle extra gravy over everything. Garnish with extra chopped herbs and a grind of black pepper.