Place sugar + water in a saucepan. Heat gently until the sugar has dissolved, stirring occasionally.. Boil rapidly for about 1 minute until syrup reaches the thread stage. Test by placing a little syrup between 2 teaspoons. When pulled apart a thread of syrup should form. Whisk egg yolks and pour in a steady stream of syrup whisking all the time. Continue to mix until mixture is thick and pale. Beat the butter in a seperate bowl untill pale and fluffy. Add the egg mixture a little at a time, beating or whisking gently after each addition until all the egg mixture has been incorporated. Add any flavourings at this stage if required and use at once.
When I make icing for my cakes I use 1 cream cheese with a 1/4c. icing sugar 1 1/2 tsp. of butter and 1/2 tsp Vinalla.whip it all together if you have any left over you can freeze it We are diebitics and we have no problems.