Boil Potatoes:

Put the peeled and cubed potatoes in a big pot of salted water. Boil until a fork pierces them easily, roughly 15–20 minutes.

Mix Meatball Ingredients:

While the potatoes cook, in a large bowl mix the ground beef, breadcrumbs, egg, grated onion, garlic, Worcestershire sauce, Dijon mustard, salt, and pepper. Use your hands to combine gently; avoid overmixing to keep the meatballs tender.

Form Meatballs:

Form the mixture into uniform balls approximately 1 ½ inches across. Arrange them on a tray lined with parchment.

Sear Meatballs:

Warm a large skillet over medium heat. Add a little oil if needed, then sear the meatballs on all sides, doing batches if needed to prevent overcrowding. After browning, take them out and set aside.

Make Onion Gravy:

In the same skillet, melt the butter and cook the sliced onions slowly until they soften and start to caramelize. Dust with flour and stir for about a minute to cook out the raw flavor. Slowly pour in the beef broth while whisking continuously to form a smooth gravy. Mix in Worcestershire sauce and thyme.

Simmer Meatballs in Gravy:

Put the meatballs back into the skillet, spooning gravy over them. Lower the heat and simmer gently for 10–15 minutes until the meatballs are fully cooked and the gravy thickens.

Mash Garlic Potatoes:

Drain the potatoes and return them to the hot pot. Add butter, warm milk, minced garlic, parsley, thyme, and salt. Mash until creamy and smooth. Adjust seasoning as desired.

Plate with Gravy:

To serve, spread a generous layer of garlic herb mashed potatoes on each plate. Top with the meatballs and a generous amount of rich brown gravy.