Trim the very top and bottom off the leek. Halve it and rinse out any grit. Finely slice it. Trim, peel and dice the carrot and parsnip. Trim and finely chop the celery. Warm a pan for 1 min. Add 1 tbsp oil and the leek, carrot, parsnip and celery. Season. Cover. Cook over a low heat for 10 mins till the veg look glossy and are sweet.
While the veg cook, finely chop the tomatoes. Peel and grate or crush the garlic. Dissolve the stock cube in 1 ltr boiling water (or use 1 ltr hot homemade stock). Stir the tomatoes, garlic and stock into the veg.
Break the spaghetti into the pan. Cover the pan. Simmer for 5 mins. While the soup simmers, shred the kale into ribbons, discarding any thick cores. Add the kale to the pan. Simmer, without the lid on, for 5-8 mins till the pasta and kale are cooked. Taste and add more salt and pepper if you think it needs it.