In a heavy non-stick frying pan, melt the butter over a very low heat. Meanwhile in a small bowl, stir the eggs adding the lemon juice and water, using a fork, until thoroughly blended and pale yellow, 1 minute. Using a large serving spoon, add the mixture to the (melted) butter by spoonfuls, constantly whisking or stirring while you add it. It will start to thicken in about 1 minute. Thickening will start in the center first. When this happens, remove the pan from the heat and continue whisking until the mixture is thick, 30 seconds or so. (If you leave it over the heat any longer, it might curdle. If it’s not thick enough, place back on the heat for several seconds, stirring). Add the salt and cayenne. Serve or hold over warm water briefly.