National Lemon Bar Day is observed worldwide every October 15 to celebrate the popular dessert known as lemon bars. This holiday was established in 2019 by Michael McCarthy, who aimed to promote lemon bars after discovering many people had never tasted them. Lemon bars, also referred to as lemon squares, consist of a shortbread crust topped with a lemon curd made from eggs, sugar, lemon juice, and zest. The celebration encourages people to bake lemon squares and share them with family, friends, and coworkers. Additionally, participants can host bake sales for charitable causes and share their creations on social media using the hashtag #NationalLemonBarDay. The dessert itself has roots in both shortbread and lemon curd, with the first recorded lemon bar recipe published in the Chicago Daily Tribune in 1963.