Preheat your oven to 180 C, or if you choose to pan fry these, omit this step.
In a large bowl, mix the meatball ingredients until completely combined. Form into golf ball size meatballs and place on a baking sheet pan or a rack on a sheet pan, just place on a plate if you are going to pan fry these.
To cook these, baking is preferred, bake for 20 to 30 minutes, cut one in half to make sure they are cooked through. Pan frying may result in meatballs falling apart.
In a large non stick skillet, add about a tablespoon of butter and olive oil and heat, then add the onion and cook until golden brown and softening. While doing this, add 1/2 cup beef stock to the corn starch to make a paste.
When the onions are cooked, add 2 cups of beef stock to the skillet, the Worcestershire sauce, ketchup, and mustard. Bring to a gentle boil and add the cornstarch mixture. Return the meatballs to the pan, reduce the heat to low, simmer for 10 minutes or until meatballs are cooked through sauce is thick, use more beef stock as needed if the sauce is too thick.
Serve meatballs and the gravy over pasta and sprinkle with fresh chopped parsley.