Pour enough oil in a heavy large saucepan to reach the depth of 3 inches. Heat the oil over medium heat to 350 degrees F.
Stir the eggs, risotto, Parmesan, and 1/2 cup of the bread crumbs in a large bowl to combine. Place the remaining breadcrumbs in a medium bowl. Using about 2 tablespoons of the risotto mixture for each, form the risotto mixture into 1 3/4-inch-diameter balls. Insert 1 cube of mozzarella into the center of each ball. Roll the balls in the bread crumbs to coat.
Working in batches, add the rice balls to the hot ail and cook until brown and heated through, turning them as necessary, about 4 minutes. Using a slotted spoon, transfer the rice balls to paper towels to drain. Season with salt. Let rest 2 minutes. Serve hot.
Bring the broth to a simmer in a heavy medium saucepan. Add the porcini mushrooms. Set aside until the mushrooms are tender, about 5 minutes. Keep the broth warm over very low heat.
Melt the butter in a heavy large saucepan over medium heat. Add olive oil. Add the onions and saute until tender, about 8 minutes. Add the white mushrooms and garlic. Using a slotted spoon, transfer the porcini mushrooms to a cutting board. Finely chop the mushrooms and add to the saucepan. Saute until the mushrooms are tender and the juices evaporate, about 5 minutes. Stir in the rice and let it toast for a few minutes. Add the wine; cook until the liquid is absorbed, stirring often, about 2 minutes. Add 1 cup of hot broth; simmer over medium-low heat until the liquid is absorbed, stirring often, about 3 minutes. Continue to cook until the rice is just tender and the mixture is creamy, adding more broth by cupfuls and stirring often, about 28 minutes (the rice will absorb 6 to 8 cups of broth). Stir in the peas. Mix in the Parmesan. Season with salt and pepper, to taste.