Add oil, onion, celery, and carrot to a medium pot over medium heat. Season with a pinch of salt to taste. Stir and cook until the vegetables sweat, about 5 minutes. Add tomato paste and cook until it caramelizes in the pan, 5 minutes. Add wine to deglaze the pan. Cook the wine to "au sec"—until the alcohol is cooked out and the pan is almost dry—5 minutes. Add the turkey neck to the pot, then the pan drippings and chicken stock. Bring to a boil; then lower heat and reduce the liquid by half, about 10 minutes.
After reducing, strain the stock, discard the solids, and return the stock to the stovetop. Place half of the croissants into the pot so they absorb some of the liquid. Put the mixture in a blender and puree. Add more croissants as needed to thicken the gravy. Season with salt to taste.