Swedish Meatballs

olive oil (, divided)

onion (, diced)

ground beef ((*see note))

ground pork ((see note*))

breadcrumbs

large egg yolk

ground allspice

ground nutmeg

salt and freshly ground black pepper (, to taste)

unsalted butter

all-purpose flour

low-sodium beef broth

sour cream

Kosher salt and freshly ground black pepper (, to taste)

fresh parsley leaves (, chopped)