The galette des rois is a traditional French pastry that is typically eaten during the Epiphany, a Christian holiday that falls on January 6th.
The pastry is a large, circular cake made of flaky puff pastry and filled with frangipane, a sweet almond cream. A small ceramic charm, known as a "fève" is hidden inside the cake. Whoever finds the fève in their slice of cake is named the "king" or "queen" for the day and gets to wear a paper crown that comes with the cake.
The tradition of eating a galette des rois on the Epiphany comes from the biblical story of the Three Wise Men, or Magi, who visited baby Jesus on the twelfth day after his birth.