Put the mince, garlic, egg, nutmeg, oregano and parmesan in a bowl. Mix together with your hands until well combined, then shape into 24 mini meatballs. Heat the oil in a large pan and brown the meatballs all over. Set the meatballs aside.
Cover the porcini mushrooms with 200ml hot water and leave to soak for 10 minutes. Meanwhile, add the onion to the pan and cook for 5-6 minutes until soft. Add the garlic and cook for another 1 minute. Season well.
Add the chestnut and shiitake mushrooms and cook for 3-4 minutes until beginning to turn golden. Stir in the rice and cook for 1 minute until all the grains are coated in the mixture. Pour in the wine and turn the heat up for 2 minutes, until the wine has bubbled and reduced.
Drain and reserve the water from the porcini mushrooms. Over a medium heat, add a ladle of the porcini liquid, and allow to simmer gently for a few minutes until the rice has absorbed the liquid. Repeat, and when the porcini liquid is finished, continue this process with the stock for about 10 minutes until the rice is plump and just tender.
Add the meatballs and an extra ladle of stock to the risotto. Allow to simmer for another 12-15 minutes, adding stock if it needs more liquid, until the meatballs are cooked through.
Stir the soaked porcini mushrooms, spinach and most of the parsley through the meatballs. Sprinkle with the parmesan shavings and reserved parsley to garnish.