Cut the end of a clove of garlic and rub on the bottom of a heavy frying pan (I prefer to use cast iron but whatever you have to hand will do)
Spray a little oil and wipe around pan to coat
Put on a very low heat
Add cherry tomatoes and mushrooms to the frying pan, cover with a pan lid and allow to cook for about 20 minutes - give a quick stir around after 10 minutes and check to make sure nothing is burning (add a few drops of water if necessary). When done it should be nicely coloured.
Meanwhile, start cooking the pasta in a separate pan.
When the pasta, tomatoes and mushrooms are nicely cooked, pour some of the pasta water into the frying pan before draining and covering to prevent drying out.
Add some tomato puree and a few drops of cider vinegar to the frying pan and stir in to form a sauce.
Chop the watercress and stir in at the last minute just long enough to heat through a little and then season to taste.
Put pasta into a serving dish and cover with sauce.