on 16 January 1985. Economy Cuisine Noirmoutier is home to the most expensive potatoes in the world. Known as "La Bonnotte", only around 100 tons of this top quality potato are cultivated annually and it is harvested only on the island Noirmoutier. The cost of one kilogram can reach €500 (US $322 per pound), but the potatoes are normally sold for around €70 per kilo (US $45 per pound). The cost is attributed to the fact that this type of potato is almost extinct because it must be harvested by hand. The potato fields also require fertilization by seaweed in a climate shaped by the nearby sea. The presence of algae and seaweed in the soil is responsible for the potato's earthy and salty flavor. Because the variety is delicate and its tuber remains attached to its stem, the potato must be picked and not torn. The potatoes are generally served in top class restaurants in France and the Netherlands in mid-May. The commune was also part of the 2005 Tour de France and 2011 Tour de France. Landmarks The Château de Noirmoutier is one of the town's major landmarks and is run by the commune government, It has been listed as a monument historique by the French Ministry of Culture since 1994. The first traces of the castle appeared in 830 with the construction of a castrum by the abbot Hilbold, from the monastery of Saint-Philbert. It served to defend the monks and the island's population from the Vikings. The castle was rebuilt in stone in the 12th century by the feudal power who was trying to stabilise the region, notably by preventing Norman pillaging. The island at that time was under the control of the barons of La Garnache. The keep was built by Pierre IV of La Garnache, then an enclosure equipped with towers was built around the lower courtyard. The castle resisted numerous attacks from the English in 1342 and 1360, and again in 1386 under the command of the Earl of Arundel. It fought off the Spanish in 1524 and 1588, but in 1674, it was taken by the Dutch troops of Admiral Tromp. In the 16th century, the castle was held by the La Trémoille family, then viscounts of Thouars. The castle was sold in 1720 to Louis IV Henri de Bourbon-Condé who resold it in 1767 to Louis XV. During the French Revolution,