Swedish Meatballs (Svenska Kottbullar)

Name: Swedish Meatballs (Svenska Kottbullar)
Prep time: 25 min
Cook time: 1 h
Total time: 1 h 25 min
Cuisine: European
Ingredients: 2 slices day-old white bread, crumbled; 0.5 cup heavy cream; 1 teaspoon butter; 1 small onion, minced; 0.66666668653488 pound ground beef; 0.33333334326744 pound finely ground pork; 1 egg; 1 tablespoon brown sugar; 1 teaspoon salt; 0.25 teaspoon ground black pepper; 0.25 teaspoon ground nutmeg; 0.25 teaspoon ground allspice; 0.125 teaspoon ground ginger; 1 tablespoon butter; 0.25 cup chicken broth; 3 tablespoons all-purpose flour, or as needed; 2 cups beef broth, or as needed; 0.5 (8 ounce) container sour cream