Mix the cornflour and water and stir into the casserole. Add the leeks and stir well. Top the chicken mixture with the potato dumplings, overlapping them slightly, so they almost cover the filling.
Heat half of the oil in a large flameproof casserole dish in two batches for ... Meanwhile, to make the kale mashed potato, place the potatoes into a large saucepan and cover with cold water.