Prepare the Turkey Meatballs: Preheat your air fryer to 400°F (200°C). In a medium bowl, combine the ground turkey, chopped onion, finely chopped fresh rosemary, dried sage, dried thyme, salt, and black pepper. Use your hands to mix just until the ingredients are combined. Be careful not to overmix, as this can make the meatballs tough.
Air Fry the Meatballs: Roll heaping teaspoons of the turkey mixture into balls. Place them on your air fryer tray, ensuring there's enough space between each meatball for air to circulate evenly. Air fry for 15 minutes, or until cooked through and golden brown. Once cooked, remove the meatballs from the air fryer and set them aside.
Thicken the Sauce: In a small cup, whisk together the cornstarch and cold water to create a smooth slurry. Add this slurry to the pot of buffalo sauce, stirring constantly. Let the sauce simmer for just a minute or two until it thickens enough to coat the back of a spoon.
Assemble and Serve: Place the cooked turkey meatballs in a large bowl. Pour the thickened buffalo sauce over them and toss gently until all the meatballs are evenly coated. Serve hot and watch them disappear!