For the meatballs:
1 cup breadcrumbs
2 tablespoons unsalted butter
1/3 cup minced white onion
2 cloves garlic, minced
1/4 teaspoon ground allspice
Kosher salt and freshly ground white pepper
1/2 cup milk
1 teaspoon Worcestershire sauce
3/4 pound lean ground beef
1/2 pound lean ground pork
1 large egg plus 1 egg white, beaten
Vegetable oil, for brushing

For the gravy:
2 tablespoons unsalted butter
2 tablespoons all-purpose flour
1 1/2 cups low-sodium beef broth
1 teaspoon Worcestershire sauce
1/4 cup heavy cream
Kosher salt and freshly ground black pepper
2 tablespoons chopped fresh parsley (optional)

Lingonberry jam, for serving (optional)