How to Make It
In a medium saucepan, heat the olive oil. Add the onion an a generous pinch of salt and cook over moderately-high heat, stirring occasionally with a wooden spoon, until the onion is translucent, about 2 minutes. Add the rice and the ham and toast for 1 minute. Lower the heat to moderate and add 1/2 cup of the chicken stock, stirring frequently, until it is nearly absorbed. Continue adding stock, 1/2 cup at a time, and stirring constantly until it is nearly absorbed before adding more. The risotto is done when the rice is tender and the liquid is creamy, about 15 minutes. Transfer the risotto to a bowl and let cool completely in the refrigerator.
Line a rimmed baking sheet with parchment paper. When the risotto is cooled completely, fold in the 1 cup of parmesan, the egg, egg yolk and 1/2 teaspoon of salt. Fill a small bowl with water. Using wet hands, form 2 tablespoons of the risotto into a ball. Make a small indent in the ball and place 1 teaspoon of the diced mozzarella in the center. Pinch the risotto closed around the mozzarella and transfer to the prepared baking sheet. Repeat with the remaining risotto and mozzarella. You will have about 16 arancini.
In a large saucepan, heat 2 inches of canola oil to 350°. Spread the breadcrumbs in a shallow bowl. Roll the arancini in the breadcrumbs until evenly coated, shaking off any excess. Fry the arancini until very golden brown, about 2 minutes. Transfer to a paper towel-lined plate and season with salt. Garnish the arancini with parsley and more parmesan and serve immediately.