In a small bowl, pour the milk over the breadcrumbs and let soak for 2–3 minutes.

In a large bowl, combine the soaked breadcrumbs, ground beef, egg, finely chopped onion, minced garlic, Worcestershire, ketchup, Dijon, salt, pepper, and parsley.

Gently mix with clean hands or a spoon until ingredients are evenly combined. Don’t overmix — it keeps the meatballs tender.

Shape the mixture into 1 1/4–1 1/2 inch meatballs (about golf-ball size). You should get roughly 14–18 meatballs depending on size.

Place formed meatballs on a baking sheet or plate while you heat the skillet.

Heat 2 tablespoons of oil in a large skillet over medium-high heat.

Add the meatballs in a single layer, careful not to overcrowd — brown in batches if necessary.

Brown on all sides, rotating gently, until a golden crust forms, about 6–8 minutes total. They don’t need to be cooked through at this stage. Remove meatballs to a plate and set aside.

In the same skillet, reduce heat to medium and add butter. Add sliced onions and cook until translucent, about 3–4 minutes.

Add mushrooms and cook until they release their juices and start to brown, about 6–8 minutes. Add the garlic and cook an additional 30 seconds.

Sprinkle the flour over the mushroom mixture and stir for 1–2 minutes to cook out the raw flour taste.

Gradually whisk in the beef broth, scraping any browned bits from the pan. Add Worcestershire.

Bring to a simmer; the sauce will start to thicken. Stir in the cream if using for a silkier sauce. Season with salt and pepper to taste.

Return the browned meatballs to the skillet, nestling them into the gravy. Cover and simmer on low for 10–12 minutes until meatballs are cooked through (internal temp 160°F) and the flavors have married.

If the gravy gets too thick, thin with a splash of broth. If it’s too thin, simmer uncovered until reduced to your liking.

Plate the meatballs over mashed potatoes, egg noodles, or rice. Spoon extra mushroom gravy over everything and sprinkle with chopped parsley. Enjoy immediately.