In a large bowl, combine the ground beef, chopped onion, garlic, egg, breadcrumbs, parsley, Worcestershire sauce, salt, and pepper. Mix well until everything is combined.
Roll the mixture into small balls (about the size of a golf ball).
Heat the olive oil in a pan over medium heat. Add the mince balls and fry until browned on all sides. Remove from the pan and set aside.
Make the Creamy Mushroom Sauce:
In the same pan, melt the butter over medium heat.
Add the sliced mushrooms and cook until soft and browned (about 5 minutes).
Stir in the minced garlic and cook for another minute.
Pour in the beef stock and bring to a simmer. Let it reduce slightly.
Add the cream and Dijon mustard, stirring well to combine.
Season with salt, pepper, and thyme/rosemary if using.
Let the sauce simmer on low heat until it thickens slightly.
Combine:
Return the browned mince balls to the pan, coating them in the creamy mushroom sauce.
Simmer for another 5-7 minutes to allow the mince balls to absorb the flavours.
Serve:
Serve the mince balls and creamy mushroom sauce over mashed potatoes, pasta, or steamed veggies.
Garnish with a sprinkle of fresh parsley for a pop of colour.