Heat a large skillet with a bit of oil or butter.
Add all meatball ingredients to a large mixing bowl and mix together with your hands very well.
Shape into 1" meatballs.
Add all of the meatballs to the hot skillet and cook for about 2 minutes on each side.
Set the meatballs aside on a plate (they will not be cooked in the middle at this point, that's ok).
Use the same skillet to make the gravy - add 4 T butter to the skillet.
When the butter is browned, whisk in the flour to make a roux.
Let the roux bubble for a minute or 2, being careful not to let it burn.
Slowly begin pouring in the beef bone broth, whisking the whole time.
Pour in cream, add salt & pepper, whisking while doing so.
Return the meatballs to the gravy right away and let them finish cooking while the gravy simmers and thickens.
If making with mashed potatoes, mash and seasn the potatoes now.
After 10 minutes or so, the gravy should be thick and the meatballs cooked through, serve over top of mashed potatoes & with fresh parlsey.