It's Basically french recipe , sometimes it's called sauce Chantilly, different places , different names :)
Makes 275 ml /10 fl oz
5 ml /1 tsp lemon juice
salt and white pepper
100 g /4 oz butter, softened
4 large egg yolks
75 ml /5 tbs thick cream, whipped
1- Place the lemon juice in the top pan of a double boiler, with 15 ml /1 tbls cold water, and salt and white pepper to taste.
2- Divide the butter into 4 equal pieces. Add the egg yolks and one quarter piece of the butter to the liquid in the top of the double boiler and place over hot, but not boiling water. Stir the mixture rapidly and constantly with a wire whisk until the butter is melted and the mixture begins to thicken.
3- Add another quarter piece of butter and continue whisking, As the mixture thickens and the second piece of butter melts, add the third piece of butter, stirring from the bottom of the pan until it is melted. Be careful not to allow the water over which the sauce is cooking to boil at any time. Add the rest of the butter, beating until it melts and is incorporated in the sauce.
4- Remove the top part of the saucepan from the heat and continue to beat for 2-3 minutes. Replace the saucepan over hot, but not boiling water for 2 minutes more, beating constantly. By this time the emulsion should have formed and your sauce will be rich and creamy.
5- Pass the sauce through a sieve. Just before serving, fold in the shipped cream, and season to taste with a little more salt and white pepper if necessary.
* This delicious sauce makes the perfect accompaniment to tish but can also be served with steamed vegetables such as asparagus or calabrese. The sieving can be omitted, but it is a way of making sure that any thread of egg white is removed. It also gives the sauce a special gloss. Be sure to add the cream only at the last moment before serving.