In a large bowl, mix together the beef, breadcrumbs, garlic, onion, egg, nutmeg, allspice, salt, pepper and parsley until fully incorporated. Roll the mixture into equal sized balls.
In a large, deep skillet, heat the olive oil over medium heat. Once hot, add the meatballs to the skillet in batches. Roll them around with a wooden spoon every couple of minutes to evenly brown the outside while they cook through. Once they're done, remove them to a towel lined plate and tent some foil over them. Set them aside.
Drain any excess fat from the skillet, but leave any charred bits that are in there from the meatballs. Increase the heat to medium-high and add the 3 tbsp of butter. Once it's melted, whisk in the flour and cook while whisking for a minute or so. Then slowly add in the broth while whisking until it's all incorporated and smooth. Whisk in the Worcestershire, Dijon and seasonings and let this come to a simmer.
Let it simmer until it thickens, stirring occasionally, then whisk in the sour cream. Add the meatballs back to the skillet and let them simmer in the sauce for about 10 minutes, until everything is heated through. Serve immediately (We just usually toss it in with egg noodles, then serve).
