Soak dried porcini mushrooms in 1 cup of hot water for 20 minutes and allow to rehydrate. Drain mushrooms, reserving soaking liquid. Chop mushrooms into pieces and set aside.
In a heavy-based frying pan, heat 2 tablespoons of butter. Sauté onion for 5 minutes, then add garlic and cook for another minute, stirring constantly.
Add rice to frying pan and cook for a couple of minutes, stirring constantly, until rice starts to turn translucent. Pour in wine and bring to a boil, then reduce to a simmer for a minute.
In a small saucepan, heat stock and liquid from the mushrooms. Add 1/2 cup of liquid at a time to the rice, stirring each time, until all liquid has been used and rice is almost tender.
Stir in chopped mushrooms, parmesan cheese and parsley into risotto. Season with salt and pepper.
Spread rice onto a baking sheet and put into fridge to cool. Once cool, roll rice into golf-ball sized balls and stuff with a piece of mozzarella. Place back in fridge for at least 30 minutes to set.
Put flour, eggs and panko bread crumbs in three separate balls. Dip each ball into flour (shaking off excess), then egg, then cover in breadcrumbs
Preheat the air fryer to 370˚F (187˚C). Place batch of arancini balls in air fryer and cook for 6 minutes. Increase temperature to 400˚F (200˚C) and cook for another 3 minutes until golden on the outside. Repeat till all balls are cooked. Serve immediately.