First, cut leeks into 1 cm disks and soak in cold water for 20 minutes, to remove any soil trapped between the layers.
Remove the skins from chicken thighs and brown in hot olive oil. Transfer to a shallow casserole dish. Drain the leeks
and fry these for a few minutes, until starting to soften, then transfer to the casserole dish with the chicken.
Make a cheese sauce by melting a Tbs butter with a Tbs flour, cooking over a low heat for a few minutes, before stirring
in whole milk to make a thick white sauce. Season with freshly ground black pepper and stir in a good handful of grated
strong cheddar cheese until melted. Pour this over the chicken and leeks, sprinkle with some more grated cheddar and bake
in a 170°C oven for about 30 minutes, until the chicken is cooked and the top golden brown. Serve with new potatoes,
halved, parboiled, then roasted in the oven alongside the chicken, garnished with parsley and accompanied by a green veg.