Melt the butter and fry the sliced onion to a golden colour. Remove the onion from the pan and, in the same butter in which the onion was fried, put in the rice and lentils and cook till all the butter has been absorbed. Then add the ginger and other seasoning ingredients, cover with hot water, put the lid on the saucepan and simmer very slowly till the water has been completely absorbed. Stir occasionally with a wooden spoon and shake the pan, so that the kedgeree will not burn. Serve very hot, with the fried onions strewn over the dish.