{gâteau des Rois}

What a wonderful tradition: A King's Cake on the Day of the Ephiphany

A king cake (sometimes rendered as kingcake, kings' cake, king's cake, or three kings cake) is a type of cake associated with the festival of Epiphany in the Christmas season in a number of countries, and in other places with Mardi Gras and Carnival.

It is popular in Christmas season in France, Belgium and Switzerland (galette/gâteau des Rois), Portugal (Bolo Rei), Spain (Roscón de Reyes and in Catalonia called tortell), Greece and Cyprus (vasilopita) and Bulgaria (banitsa). In the United States, which celebrates Carnival ranging from Pensacola, Florida to East Texas, centered on New Orleans it is associated instead with Mardi Gras season traditions.

The cakes have a small trinket (often a small plastic baby, sometimes said to represent Baby Jesus) inside, and the person who gets the piece of cake with the trinket has various privileges and obligations (such as buying the cake for next year's celebration). From Wikipedia.