Peel and cube the potatoes, place in a large pot, cover with cold, salted water, and boil for 12-15 minutes until fork-tender. Drain and return to pot.

Add butter and warmed milk to drained potatoes. Mash until smooth and creamy, seasoning with salt. Keep warm.

In a skillet, cook ground beef over medium heat until browned, about 5-7 minutes. Add onion and garlic, sautéing for 2-3 minutes until fragrant.

Sprinkle flour over beef mixture, stir to coat, and allow to cook for 1 minute. Gradually whisk in beef broth, adding Worcestershire sauce and onion powder.

Simmer the gravy for 5-7 minutes until thickened, adding more broth if it becomes too thick. Optionally stir in butter before serving.

Serve mashed potatoes topped with beef gravy. Garnish with cracked black pepper or parsley if desired.