Galette de Roi

Or in English, King Cake,  is a type of cake  associated with the festival of Epiphany in the Christmas season in a number of countries. The cake has a small trinket inside and the person who gets the piece of cake with the trinket has a various previleges and obligations

The cake has a small trinket (often a small plastic baby, said to represent Baby Jesus) inside (or sometimes placed underneath), and the person who gets the piece of cake with the trinket has various privileges and obligations.

Source: King Cake Wikipedia