In a medium-sized bowl, combine ground beef, panko bread crumbs, parsley, allspice, nutmeg, onion, garlic powder, pepper, salt, and egg. Mix until combined.
Roll into 12 large meatballs or 20 small meatballs.
In a large skillet, heat olive oil and butter. Add the meatballs and cook, turning continuously until brown on each side and cooked throughout. Transfer to a plate and cover with foil.
Add butter and flour to the skillet and whisk until it turns brown.
Slowly stir in beef broth and heavy cream. Add Worcestershire sauce and Dijon mustard and bring to a simmer until the sauce starts to thicken. Salt and pepper to taste.
Add the meatballs back to the skillet and simmer for another 1-2 minutes. Serve over egg noodles or rice.
