Preheat the oven to 375 degrees F. Butter a rimmed baking sheet and set aside.
Melt 1 tablespoon of the butter in a large straight-sided skillet over medium heat. Add the onions and cook until softened but not brown, about 5 minutes. Transfer the onions to a medium bowl and let cool.
Add the turkey, bread, egg, 1 1/2 teaspoons salt, 1/2 teaspoon pepper, allspice and nutmeg to the onions and stir vigorously with a wooden spoon until the mixture becomes sticky, about 2 minutes. With clean, damp hands, roll the mixture into 1-inch balls (about 1 tablespoon) and place on the prepared baking sheet; clean and dampen hands as needed to prevent the mixture from sticking. Bake until the bottoms are slightly brown and the meatballs are firm, about 10 minutes.
Wipe out the skillet and melt the remaining 2 tablespoons of butter over medium-high heat. Sprinkle in the flour and whisk to make a paste. Add the chicken broth and continue whisking until smooth. Bring to a boil over high heat, whisking occasionally, then reduce the heat to maintain a rapid simmer and cook until the sauce has thickened, about 8 minutes. Stir in the cream, Worcestershire and half the parsley and season with salt and pepper. Add the meatballs to the skillet and cook for 5 minutes to blend the flavors. Sprinkle with the remaining parsley and serve with lingonberry jam as hors d’oeuvres or over egg noodles as a main course.