Cook the pasta according to the pack instructions, drain and set aside, reserving the cooking liquid.
Heat the oil in the saucepan you cooked the pasta in and add the onion, cook for 5 minutes or until soft and translucent. Add all of the remaining ingredients and gently heat through until the ricotta and Parmesan melt, if the sauce is too thick add a little of the pasta cooking water until it is a smooth creamy consistency.
To serve, add the pasta back to the pan and gently toss in the sauce. Can be eaten hot or cold.