Add 1 tablespoon olive oil to a large frying pan over medium-high heat. Add 50 g leek and 5-6 cloves garlic (both chopped) and sauté for a few minutes, until aromatic and softened.
At this stage, add 200 g chestnut mushrooms (chopped) and sauté, until the mushrooms have softened.
Add 230 g risotto rice to the same pan. Stir continuously for a few minutes, and cook until lightly toasted and golden. Next, add 700 ml vegetable stock or water, one ladle at a time. Stir the risotto continuously, cooking the water down completely before you add more. Repeat this process until all the stock is absorbed and the risotto rice is plump.
Season with 1 teaspoon black pepper (ground) and 1 ½ teaspoon salt.
Prepare the Arancini
Cool the risotto. Tip it from the pan onto a lined tray. Spread the risotto out. Place the tray in the fridge to cool, for a minimum of 30 minutes.
Once the risotto is cool enough to touch, form either 20 small balls or 10 large ones. Grease your hands to stop the risotto from sticking. Once done, set aside on a plate.
Take 45 g breadcrumbs and tip them onto a flat plate. Take an arancini ball and roll it in breadcrumbs, until completely coated. Repeat this process with all the arancini.
Cook the Mushroom Arancini
To bake the mushroom arancini: Preheat your oven to 200℃ (392℉). If you'd like extra-golden arancini, you can pre-toast your breadcrumbs before coating the arancini. Once the arancini are coated, arrange the mushroom arancini on a lined baking tray. Spray the arancini with oil and bake for around 20 minutes, until golden.
To air-fry the mushroom arancini:Preheat your air-fryer to 200℃ (392℉). Spray the air-fryer basket with oil and arrange the breaded arancini in the basket. Leave ample space between the arancini! Cook for around six minutes, then spray with more oil, turn, and cook for another 6 minutes, or until golden. Repeat this process with the remaining arancini.
To deep-fry the mushroom arancini: Preheat the oil in your deep fat fryer 190℃ (350℉). Once the oil comes to temperature, gently lower the arancini into the hot oil. Work in small batches so as to not overcrowd the oil. Fry the arancini until golden brown, remove from the oil with a slotted soon, and drain on kitchen towels. Repeat the process as needed.