In a large skillet over medium heat, sauté the onions in the olive oil until they begin to soften. Remove the sausage from its case and add to the onion, breaking the sausage apart with a fork. Cook the sausage and onions until the onions are golden. Puree the tomatoes in a blender or food processor, and add to the sausage mixture. Add salt and pepper to taste. Cook over low heat for about 30 minutes until reduced, and then add the cream. Cook for an additional 5 minutes until further reduced. Add the peas and mix well.
Meanwhile, bring a large pot of salted water to a boil. Cook the pasta until just shy of al dente. Drain the pasta and add it to the tomato mixture. Stir together over low heat for about a minute. Serve immediately with a sprinkle of Parmigiano.