What ingredient must French vanilla ice cream have in it to distinguish it from regular vanilla?

Vanilla is frequently used to flavor ice cream, especially in North America and Europe. Vanilla ice cream, like other flavors of ice cream, was originally created by cooling a mixture made of cream, sugar, and vanilla above a container of ice and salt. The type of vanilla used to flavor ice cream varies by location. In North America, consumers are interested in a more prominent, smoky flavor, while in France, they want a more anise-like flavor.

By the early eighteenth century, recipes for ice cream had appeared in France. According to Frozen Desserts: The Definitive Guide to Making Ice Creams, Ices, Sorbets, Gelati, and Other Frozen Delights, the French transformed ice cream into a smoother and richer food with the addition of eggs or egg yolks in the recipe. The first ice cream recipes recorded by the French in the early eighteenth century did not include egg yolks. However, by the middle of the eighteenth century, French recipes for ice cream started to include egg yolks.

When the use of vanilla in foods and drinks became independent of cacao, it became more prominent in French recipes. The French used vanilla to flavor French vanilla ice cream. Vanilla ice cream was introduced to the United States when Thomas Jefferson discovered the flavor in France and brought the recipe to the United States. During the 1780's, Thomas Jefferson wrote his own recipe for vanilla ice cream. The recipe is housed at the Library of Congress.