The Book of Household Management by Mrs. Beeton

359. GRAVIES AND SAUCES SHOULD BE SENT TO TABLE VERY HOT; and there is

all the more necessity for the cook to see to this point, as, from their being usually served in small quantities, they are more liable to cool quickly than if they were in a larger body. Those sauces, of which cream or eggs form a component part, should be well stirred, as soon as these ingredients are added to them, and must never be allowed to boil; as, in that case, they would instantly curdle.