|Source: Cour grand-ducale|
The pretzel represents an Easter tradition unique to Luxembourg and part of Bretzelsonndeg, or Pretzel Sunday, which is the fourth Sunday of Lent. According to tradition, this Sunday is an opportunity for young men to demonstrate their interest in young ladies by giving them a decorated pastry in the shape of a pretzel. In the event that the young lady reciprocates the interest, she can give the young man a chocolate egg in return, on Easter Sunday. The size of the response gift also tends to correspond to the original: that is, the young lady gives a large egg if the young man has given her a large pretzel cake.
However, the tradition states that everything is reversed during a Leap Year: the young lady presents the pretzel, while the young man presents the chocolate egg.
This particular exchange of gifts may have originated with young people expressing their interest in one another, but it's now more universal, and married couples also participate (with the assumption that, among spouses, the chocolate egg is always given in response to the pretzel).