Starting from base, bend each asparagus spear and snap off where it breaks naturally. Discard ends. Cut asparagus into 1 inch pieces. Set aside.

Pour broth into saucepan; bring to simmer. Reduce heat to low, keep hot.

Heat oil in heavy large saucepan over medium-high heat. Add onion and cook until tender, stirring frequently, about 5 minutes. Add rice and half of prosciutto and stir 2 minutes. Add 3/4 of broth to saucepan and adjust heat so that the liquid simmers. Cook 10 minutes, stirring frequently. Add asparagus and continue cooking until rice is tender but still slightly firm to the bite and mixture is creamy, stirring frequently and adding remaining broth by 1/4 cupfuls as necessary, about 15 minutes. Add peas and green onions and stir until heated through, about 2 minutes.

Set aside 2 tablespoons basil and 1 tablespoon prosciutto for garnish. Stir remaining basil and prosciutto and 2 cups parmesan cheese into risotto. Season to taste with salt and pepper. Garnish with reserved basil and prosciutto. Serve immediately, passing additional parmesan cheese separately.