Puree half of the peas in a food processor and set aside with the whole peas.
In a saucepan, heat the chicken broth and keep warm. Grease a 2-quart casserole and set aside.
In a large saucepan, heat 3 tablespoons of the butter over medium heat. Stir in the onion and cook until translucent, about 4 minutes. Add the rice and stir well to coat the grains with butter. Add 1 cup of the chicken broth to the rice, lower the heat slightly and stir until the broth is absorbed. Continue adding broth in 1/2 cup increments, letting the rice absorb the liquid (about 3 minutes) after each addition, and stirring almost constantly, until the rice is cooked, 20 to 25 minutes. The finished rice will be creamy but still firm to the bite.
A few minutes before the risotto is done, stir in the pureed and whole peas. Turn on the broiler.
Remove the cooked rice from the heat and stir in the remaining 2 tablespoons of butter and 3/4 cup of grated Parmigiano-Reggiano. Season with salt and pepper. Stir the remaining 1/4 cup of grated cheese and the bread crumbs together. Transfer the risotto to the prepared casserole dish and top with the bread crumb mixture. Place the dish under the broiler about 6 inches from the heat source and broil for about 2 minutes, or until the top is golden. Serve immediately.