Pour the canned tomatoes into a bowl and gently press to break them down using a fork.
Remove the skin from the guanciale with a knife, but leave the fat.
Cut the guanciale into thin strips, then into bite-size pieces.
Make a shallow cut in the Italian sausage, then peel off the skin. Press the sausage meat flat with the side/tip of the knife and break it into smaller pieces.
Put three tablespoons of extra virgin olive oil in the frying pan. Add diced onion and cook for up to 7 minutes on medium heat (less if it starts to brown too much).
When the onion turns golden brown, add the guanciale, and once this is crispy add Italian sausage. Stir continuously making sure it is cooked all over.
Add some more extra virgin olive oil and allow it to cook through.
When sausage becomes greyish brown, add peeled tomatoes. Stir gently and cook for 15 minutes on medium-low heat.
Add a touch of salt and press down on the tomatoes to release the juice. Leave to cook for 15 more minutes.