In European and American dining it's traditional to have a small course, followed by a main dish, then a sweet dessert. When and how did this convention arise and why has it become so dominant that basically every restaurant menu in the US is divided this way?
This style is technically called service à la Russe and, as the name suggests, Europe and America adopted it from Russia. Originally it would have comprised many courses delivered consecutively, although over time it has developed into the style we are familiar with today.
Previously, fine dining would have been service à la Française. In this style all the food being served is presented at the table in one go, primarily to show the abundance of the spread. The transition between these two styles began in Europe during the early 1800s.
Marie-Antoine Careme (1784-1833) was the grandfather of French gastronomy and chef to the kings of Europe; he is one possible source of inspiration for the change. Having cooked for Napoleon I of France and George IV of Great Britain, Careme was subsequently employed for a short while by Tsar Alexander I of Russia. It is quite possible that he became more familiar with the Russian service style and it is often suggested that he played a role in its European introduction. Careme's influence is hard to overstate: it was on much of his work that Auguste Escoffier later formulated modern style cuisine.
Alexander Kurakin (1752-1818) was an ambassador for Tsar Alexander during the early 1800s, first in Austria and then in France. His social circles included several people that Careme will have met and cooked for. Kurakin was a lavish and bombastic man who, while in Paris, may well have instigated the Russian service of his homeland instead of the local French service style. In any event, one of these two men (or both) were likely responsible for influencing the transition at its earliest stage.
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