Shell your peas but don't throw the pods away. Rinse them and put them in a stockpot with a sliced onion and two sliced carrots, a pinch of salt and just enough water to cover. Simmer for a good half hour or more until you have a flavorsome broth.
Now make a soffritto with very finely chopped onion, pancetta and parsley (a food processor makes short work of the task) gently sautéed in butter and a bit of olive oil. (Some recipes call for a bit of garlic) When the onion is soft and translucent, add your shelled peas and a ladleful of the pea broth. Cover and gently simmer the peas over low heat until they are almost tender.
Now add the rest of the broth and the rice—preferably Vialone nano but Arborio will do in a pinch—and continue simmering until the rice is tender, stirring from time to time. Add more broth or water if the rice dries out—but this is not a risotto where you should be adding liquid little by little. Remove from the heat and stir in a nice portion of freshly grated parmesan cheese and another nut of butter, continuing the stir until the cheese is entirely incorporated and the rice has taken on a nice, creamy consistency. Serve immediately. The dish should be rather liquid and flow easily, all'onda or 'like a wave' as they say in Italian, the typical of the rice dishes of the Veneto. Some versions are even wetter, almost a soup.