Start by adding the onion into a large saucepan with a tbsp of oil or the reserved fat from a turkey roast. If you do have reserved fat from Christmas/ a roast, this will add an additional layer of flavour & help to colour the broth. Sweat the onions for 5 minutes before adding the carrots & celery.
Continue to gently fry the carrots and celery for a further 5 minutes. The pieces should be medium sized as the broth will be simmering for a while and we want the veg to be able to hold their own and not turn into mush. After this 5 minutes, add the garlic to fry for a couple of minutes before pouring the stock into the pan.
Place the fresh thyme and parsley stalks into the saucepan, not stirring so they still float & hang around at the top of the pan. If you have a cooking string then tie them up for ease with the removal process (I didn’t but it’s not too hard to fish them out at the end). For added richness/ colour for the broth, add the onion skins (washed) into the pot. This will provide that golden hue that we want in a noodle soup. Simmer covered for 30 minutes/up to 45 minutes, if you have time.
After this time, remove the fresh thyme, parsley stalks and onion skin from the surface and flavour with soy sauce and season generously with salt and pepper. It’s a lot of liquid so this isn’t the time to be stingy with the salt.
Add the cavolo nero, spaghetti and turkey to the pot to cook until the spaghetti is al dente. Add a squeeze of lemon. For the final few minutes of cooking, add the cornflour, combined with some water to form a paste, into the pot to thicken the broth. Serve with fresh parsley and red pepper flakes.