A little trouble to make but you can taste the difference.
Mix together the flour, sugar, mustard, salt and egg yolks. Add the evaporated milk; mix well and turn into a double boiler. Cook over boiling water, stirring con-stantly, until the mixture is heated through. Add the cream and vinegar alternately, a few drops at a time. Stir and beat the mixture while it cooks, until thick and smooth: Remove from the stove, and stir in the butter. When the butter is melted, strain the dressing.