Pre-heat a large skillet over medium heat.
Add 1 Tablespoon of olive oil followed by the onions and garlic. Cook until soft and translucent (approx. 3 minutes).
In a large mixing bowl, combine the cooked onions, meat, bread crumbs, egg yolk, garlic and allspice. Season to taste with salt and pepper.
Using clean hands, mix until combined.
Form the meatballs by rolling the dough between the palms of your hands. Each meatball should be about 1.5".
Heat the same skillet back up to medium heat.
Add remaining oil followed by 6 meatballs (don't crowd the pan!). Cook until all sides are browned.
Once browned, transfer to a paper-lined cookie sheet and repeat with the remaining 6 meatballs.
After the meatballs are browned, remove the excess pan drippings, keeping only a tablespoon in the skillet.
Add the butter to the skillet and whisk in the flour until lightly browned (approx. 1 minute).
Whisk in the beef broth for about 2 minutes, until slightly thick.
Whisk in the sour cream.
Add salt and pepper to taste.
Add all 12 meatballs to the gravy and cook, turning the meatballs occasionally, until cooked throughout (approx. 10 minutes).
Garnish with parsley and serve immediately.