Originally panettone was shorter than the type pictured above. The panettone genovese still traditionally made in Genoa is very close to the medieval and renaissance version, for example. The basic recipe evolved through time with the addition of raisin, vanilla then candied orange and citron rinds. The real innovation came however in 1919 by the hand of the Milanese baker Angelo Motta, who invented a long curing process where the dough is leavened three times and kneaded two over several days. The result is the especially soft cake you can find in shops today.
Motta had to fight hard to keep control of his creation, especially with another Milanese baker called Alemagna. The competition between them lasted almost one century, leading to better and better panettoni (the plural form of the name) and a pricing war to make each cake the most convenient. Come the end of WWII, panettone was the most affordable – and tastiest – sweet on the war-weary market: this is what sealed the fate of this delicacy as a Christmas treat.