Peel and cut the Yukon gold potatoes into rough 1-inch chunks. Place them in a large pot and cover with cold, salted water. Bring to a boil and cook until fork-tender, about 15-20 minutes.

Drain the potatoes thoroughly and return them to the empty, hot pot. Let sit for 1 minute to steam off excess moisture.

Heat the half & half and butter in a small saucepan until butter is melted and mixture is warm.

Pour the warm mixture over the potatoes. Mash until smooth using a potato masher or ricer.

Stir in garlic powder, salt, pepper, and chopped parsley. If using, fold in Parmesan cheese. Keep warm.

In a large mixing bowl, combine ground beef, breadcrumbs, egg, minced onion, minced garlic, 1 tablespoon Worcestershire sauce, dry mustard (if using), thyme (if using), salt, and pepper. Mix gently until just combined.

Roll mixture into balls about 1 ½ inches in diameter, yielding about 18-20 meatballs.

Heat 2 tablespoons oil in a large skillet over medium-high heat. Sear meatballs on all sides until browned, about 8 minutes. Remove to a plate.

In the same skillet, add 2 tablespoons butter. Add sliced mushrooms and cook until soft, about 5-7 minutes. Season with salt and pepper.

Sprinkle flour over mushrooms and stir for 1 minute to make a roux.

Gradually whisk in beef broth, scraping up browned bits. Stir in 1 teaspoon Worcestershire sauce and optional red wine or A.1. sauce.

Bring to a simmer and thicken, about 5 minutes. Return meatballs to gravy, cover, and simmer for 10-12 minutes until cooked through (internal temp 165°F).

To serve, place a scoop of mashed potatoes on plates, top with meatballs and gravy.