“Beurre Extra Fin” is a classification used in France for classifying butter. As for “regular” “Beurre Fin”, the butter is made from pasteurized cream, none of which can be recovered from whey, and a maximum of 30% of the cream used overall can have been previously frozen.
In addition, Beurre Extra Fin must be made within 70 hours of the milk having been collected. The pasteurization and churning are to have been done within 48 hours after the cream having been skimmed off the milk.