Like some other French favourites (crêpes Suzette, ganache and tarte Tatin) crème au beurre was invented by accident in the 19th century.
The head chef of the Prince of Joinville had several white coloured sauces going ready to be finished in the kitchen— crème anglaise, chantilly, a butter sauce for glazing and a béchamel—and overwhelmed, he asked his apprentice to add butter to the béchamel.
But the apprentice mistakenly added the butter to the crème anglaise, whisked and let it cool and voilà! crème au beurre was born.
It’s not as easy to make (or as sweet) as American or ‘mock’ butter cream: sugar and water heated to the soft ball stage (petit boulé, 120 °C/248 °F) and slowly added to whipped egg yolks then beaten until the mixture cools, before adding beurre pommade (butter beaten to a pomade like consistancy) and silky smooth. Add any flavouring, chill and it’s ready to fill a cake.
Another name for it is pâte à bombe.
Image by Whitney