In a large mixing bowl, blend together ground turkey, panko breadcrumbs, Parmesan cheese, egg, finely chopped onion, minced garlic, fresh sage, dried thyme, salt, and black pepper. Use your hands or a spatula to mix until just combined.

Shape the mixture into 1-inch meatballs, aiming for about 24 in total. Place them on a parchment-lined tray.

In a large skillet, heat olive oil over medium heat. Add the meatballs in batches, browning them for about 2-3 minutes on each side until golden brown.

In the same skillet, add more olive oil if needed and sauté chopped onion over medium heat for about 5 minutes until soft and translucent, then add minced garlic and cook for another minute.

Stir in pumpkin puree and chicken broth to the sautéed onions and garlic, allowing the mixture to simmer for about 5 minutes.

Mix in heavy cream, Parmesan cheese, fresh sage, dried thyme, and a pinch of ground nutmeg. Let it simmer for an additional 5-10 minutes until thickened.

Return the browned turkey meatballs to the skillet, cover, and let them simmer on low heat for 15-20 minutes until cooked through.

Garnish the turkey meatballs with fresh sage leaves and a sprinkle of red pepper flakes before serving.