Line a large baking sheet with parchment paper and set aside.
In a large pot, bring the chicken broth and water to a boil. Keep it at a low boil as you proceed.
In a separate large saucepan over medium heat, add 2 tablespoons (30 ml) of extra virgin olive oil. When hot and shimmery, add the onions to the pan and lightly season with salt. Cook, stirring often, until they become tender and translucent, about 8-10 minutes.
Add the rice and continue to stir gently to coat and lightly toast in the oil, about 5 minutes. Remove the pan from the heat and add the wine. Stir to combine and return to a boil.
Using a ladle, add 1 cup (240 ml) of the broth mixture to the rice, stir continuously while keeping the mixture at a constant boil. When the liquid has been almost fully absorbed, add another ladle of hot broth. Repeat this process until you have added all, or almost all, of the broth and the risotto is just about fully cooked through.
Add the butter, Parmigiano and peas, stir until all the ingredients are thoroughly incorporated and the peas have warmed through, 1 minute more. Season with salt and pepper, to taste. Remove the pan from the heat.
To help facilitate the cooling process, spread the risotto on the baking sheet lined with parchment paper for a few minutes, or until cool to the touch. Once the risotto is at a comfortable temperature to handle, roll portions of the risotto in your hands to form balls, about 4 ounces (or so, and stuff each one with a piece of mozzarella, taking care to seal around the mozzarella well.
Place the flour, egg, and breadcrumbs in separate bowls. Coat one risotto ball first with the flour, then with the egg, and finally with the breadcrumbs. Place it back on the baking sheet lined with parchment paper. Repeat until all the risotto balls have been coated and set aside on the baking sheet.
In a large 12-inch (30-cm) heavy-bottomed skillet, heat 1 cup (240 ml) of olive oil until it is very hot, taking care not to let the oil smoke. Fry the arancini in the oil until they become golden brown all over. Use a large kitchen spider strainer to help turn and remove the arancini. Transfer each rice ball to a plate lined with paper towels to drain away any excess oil. Serve warm.
Notes
Consider adding seasoned chopped meat (great way to use leftover meat) to the center. Can serve with marinara to dip, optional.