Final answer:
The first cookbook by Taillevent, also known as Guillaume Tirel, was Le Viandier and is believed to have been compiled around the mid-14th century, though the oldest manuscripts date from the late 14th to early 15th century.
Step-by-step explanation:
The question asks about the first cookbook written by Taillevent, a historical figure closely associated with French cuisine. Taillevent was the pseudonym of Guillaume Tirel, a master chef to French royalty in the 14th century. While the comprehensive details about the exact date Taillevent wrote his influential cookbook are not provided in the reference information, according to historical sources, his well-known work titled Le Viandier has been attributed to him and is believed to have been compiled in its earliest form around the mid-14th century, specifically the 1320s or 1340s.
This would place it during the reign of King Philip VI or King John II of France. However, the oldest surviving manuscripts of Le Viandier date back to the late 14th to the early 15th century. Taillevent's cookbook is significant as it provides insight into the culinary practices and preferences of the French aristocracy during the Middle Ages.