1. Blend the dried egg and 30 ml/2 tbls of the water to a smooth cream.
2. Place the remaining water and sugar in a small heavy-based pan and dissolve over a low heat. Do not stir. When the sugar has dissolved, increase the temperature and boil steadily until the syrup forms a thin thread between 2 teaspoons dipped in the syrup (110°C/225°F on a sugar thermometer).
3. Pour the sugar syrup on to the egg mixture in a thin steady stream, whisking all the time. Continue whisking until the mixture is cool.
4. Gradually whisk the butter into the egg mixture, a little at a time, whisking well between each addition. Flavour as desired.