Risotto con Parmigiano-Reggiano

Bring broth to boil in medium saucepan. Reduce heat to low; cover saucepan. Melt 2 tablespoons butter in heavy medium saucepan over medium-low heat. Add onion; sauté until very tender but not brown, about 15 minutes. Increase heat to medium. Add rice and stir 1 minute. Add 1 1/2 cups warm broth. Boil gently until broth is absorbed, stirring frequently. Add another 1 cup broth; stir until broth is absorbed. Add remaining 2 1/2 cups broth, 1/2 cup at a time, allowing broth to be absorbed before adding more and stirring frequently until rice is tender and mixture is creamy, about 25 minutes. Stir in 2 tablespoons butter and 1 cup grated cheese. Season with salt and pepper. Transfer to bowl. Sprinkle with parsley and shaved Parmesan.