Melt about 1 tablespoon of lard in a saucepan and, when hot, add the chopped onion, the paprika or pimiento and the potatoes cut in small dice. Simmer gently without browning till the onions are of a light golden colour, and sprinkle with a little chopped parsley. Add the hot water, stir in the paprika, season with salt, bring to the boil and simmer for ½ an hour or till the potatoes are cooked. Stir in 1 tablespoon of the sour cream a few minutes before serving, and the remaining sour cream when the saucepan has been removed from the fire.