In a large pot cook penne pasta in boiling salted water until al dente. Drain well.
Meanwhile, remove casings from sausage. In a large skillet cook the sliced Italian sausage until brown. Drain excess grease with paper towels. Add chopped onion, minced garlic, and stewed tomatoes to sausage skillet. Bring mixture to a boil. Reduce heat and add the half-n-half cream. Cook until heated through.
In a large bowl toss the sausage sauce with cooked and drained pasta. Serve with shredded Cheddar cheese.