Southern Boiled Salad Dressing

Set the bottom of a double boiler with about an inch of water over medium heat and bring to a boil. While the water heats, sift the dry mustard, sugar, salt, flour into the top of a double boiler or into a stainless steel bowl which can be placed over the boiling water. Add the pepper. Gradually pour the cold water into the dry mixture while whisking constantly. When the mixture is well blended, whisk in the beaten egg yolks and vinegar. Place the pan or bowl over the boiling water and cook, whisking, until the mixture is thickened. This takes just a few minutes. Remove from the heat and whisk in the butter until melted and well combined. Whisk in the heavy cream until you have the correct consistency for your salad.