This delicious recipe comes from Elana Molokhovet’s A Gift for Young Housewives, a massive work in four volumes destined for the rising Russian middle-class, a sort of Mrs. Beeton for Russia; it sank without trace in the Revolution of 1917. The original recipe suggests keeping the carp’s blood mixed with vinegar and adding it to the sauce at the roux stage. Get the fish vendor to clean and gut the carp for you.