Melt 2 tablespoons of butter in a skillet over medium heat. Stir in the onion, and cook until the onion has softened and turned translucent, about 5 minutes. Scrape into a bowl, and set aside until cool.
Stir the sour cream together with the bread crumbs in a small bowl. In a large bowl, lightly combine the onion, eggs, ground beef, ground pork, cinnamon, cloves, nutmeg, salt, and pepper; stir in the sour cream-crumb mixture, and lightly but thoroughly mix until combined. Form the meat mixture into small balls about the size of a walnut.
Melt another 2 tablespoons of butter in a large skillet over medium-high heat. Add the meatballs, and cook until browned on all sides and no longer pink in the center, about 10 minutes.
