Preheat the oven to 400°F (200°C) and line a rimmed baking sheet with parchment paper.
In a large mixing bowl, combine the ground turkey, almond flour, 1/4 cup parmesan, beaten egg, 2 cloves minced garlic, parsley, onion powder, salt, and pepper. Mix by hand until just incorporated, avoiding overworking the meat.
Portion the mixture into approximately 16 to 18 meatballs (roughly 1.5 inches in diameter) and arrange them evenly on the prepared baking sheet.
Bake for 15 to 18 minutes, or until the internal temperature reaches 165°F (74°C). Optional: Broil for the last 2 minutes for additional browning.
While the meatballs are baking, melt the butter in a large skillet over medium heat. Add the remaining 2 cloves of minced garlic and sauté for 60 seconds until fragrant.
Whisk in the heavy cream and chicken broth. Bring the liquid to a gentle simmer and cook for 5 minutes, allowing the volume to reduce slightly.
Lower the heat to medium-low and whisk in 1/2 cup of grated parmesan cheese and the nutmeg. Stir continuously until the sauce is smooth and thickened.
Transfer the baked meatballs directly into the skillet. Toss gently to coat each meatball in the sauce. If using spinach, fold it in now and cook until just wilted.
Simmer for 2 additional minutes to allow the flavors to meld. Garnish with additional parsley and serve immediately.