1) Place the sausages into a baking tray, sprinkle with oil and roast in an oven at 200 degrees for 30 minutes.
2) Slice the onions into half moons and sautee for 10 minutes.
3) Add the chopped garlic and tomatoes to the onion pan and continue frying for 2 minutes.
4) Add the tomato purée, oregano and onion powder along with 300ml of water to the onion pan.
5) Simmer the sauce for 1 hour.
6) Add the ketchup and mix into the sauce.
6) Chop the sausages into bite size chunks and add to the onion pan.
7) Season to taste.
8) The sauce is best left overnight to mascerate before serving.
9) Serve with grated Parmesan and tagliatelle.