This section is from the book "Soyer's Standard Cookery", by Nicolas Soyer. Also available from Amazon: Soyer's Standard Cookery.
Five squares of chocolate, two cups of powdered sugar, six tablespoonfuls of milk, yolks of two eggs, one teaspoonful of vanilla.
Melt chocolate over hot water, add one-half the sugar and milk; add remaining sugar, and yolk of egg; then cook in double boiler until it thickens, stirring constantly at first, that mixture may be perfectly smooth. Cool slightly, flavor, and spread.
 
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