2 Tbsp olive oil, divided
1 onion, diced
1 pound ground beef
1 pound ground pork
1/2 cup bread crumbs
2 egg yolks
1/4 tsp ground allspice
1/4 tsp ground nutmeg
Kosher salt and freshly ground black pepper, to taste
For the Gravy:
1/4 cup unsalted butter
1/3 cup all-purpose flour
4 cups beef broth
3/4 cup sour cream
Kosher salt and freshly ground black pepper, to taste
2 Tbsp chopped fresh parsley leaves