Heat the olive oil and butter in a large pan. Fry the onion in it for about 4-5 minutes, then add the rice. Stir until all of the rice is coated with oil. Add the white wine. After this is completely absorbed, gradually add the broth. Each time, wait until all of the liquid has been absorbed before adding new ones. As soon as half of the broth is used, add the tomatoes.
As soon as the rice has the desired consistency (I cannot give an exact specification, as one likes firm rice and the other buttery soft), stir in Parma ham, peas and Parmesan and heat. Serve immediately.
Tip: after filling up, sprinkle with parmesan cheese if necessary.