3    Egg yolks
1/2 c  Sugar
1/2 ts Lemon rind; grated
1 ts Lemon juice
1 ts Vanilla (opt)
1 qt Buttermilk
1/4 c  Heavy cream; whipped (opt)

“The flavor of commercial buttermilk varies enormously from dairy to dairy.
Natural fresh buttermilk, if available, would be ideal for this unusual
summer luncheon or dessert soup, but cultured buttermilk of good flavor
will do almost as well.” With an electric beater or wire whisk, beat the
egg yolks in a large bowl. Gradually add the sugar, beating until the eggs
fall back into the bowl in a lazy ribbon when the beater is lifted. Add the
grated lemon rind and juice and the optional vanilla. Slowly beat in the
buttermilk, continuing to beat until the soup is smooth. Serve in chilled
bowls and float a spoonfull of unsweetened whipped cream on the surface of
each service if you like. Buttermilk soup is traditionally served with Oat
Cakes. (See recipe.)