Preheat oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking dish lightly with cooking spray.

Heat olive oil in a small skillet over medium heat. Add onion and garlic; cook and stir until softened, about 5 minutes. Let cool briefly, about 5 minutes.

Combine onion mixture, turkey, bread crumbs, egg, 1 tablespoon Worcestershire sauce, 1 1/2 teaspoon parsley, allspice, and nutmeg in a large bowl; mix well to combine. Form mixture into 1-inch meatballs. Transfer to baking dish.

Bake in the preheated oven until meatballs are cooked through, 25 to 30 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).

Pour beef broth into a jar with a tight-fitting lid. Add flour; seal and shake vigorously until flour is dissolved.

Pour beef broth mixture into a large skillet over medium-high heat. Add 1 tablespoon Worcestershire sauce, 1 1/2 teaspoon parsley, black pepper, and salt. Bring to a boil, stirring frequently. Reduce heat to medium and simmer, stirring occasionally, until thickened, 2 to 3 minutes. Reduce heat to medium-low; stir in sour cream and meatballs. Cover and simmer, stirring occasionally, until flavors combine, 10 to 15 minutes.