Stir well the egg yolks, sour cream, salt, sugar, mustard, lemon juice and pepper.
Put the mixture in the top part of a double boiler over steam. When the steam starts to cook the mixture, whip with the right hand and with the left hand add the olive oil drop by drop. (If you cook this over direct heat, make sure that the heat is not too high or you will make scrambled eggs out of the mixture.) Add the oil very slowly, otherwise the ingredients will not amalgamate.
While continuing to whip the sauce, add heavy cream and finally the wine.
Adjust the sugar and salt; Hungarians generally like this sauce much sweeter than do Western nations. Serve with various fish dishes, Breaded Veal Knuckles and many other dishes.