For many, March is just another month, but for others, it is the month to celebrate the Shamrock Shake. This year, McDonald’s extended the famous Shamrock shake into four new versions of the creamy treat. For a limited time, you can enjoy the new Chocolate Shamrock Shake (which is half chocolate and half Shamrock), Shamrock Chocolate Chip Frappe, Shamrock Hot Chocolate, and the Shamrock Mocha. The classic Shamrock Shake is just mint.

According to the Huffington Post, the thick beverage first appeared at McDonald’s in 1970 and was dubbed the “St. Patrick’s Day Shake” (which was quickly changed) and gave customers a new option from the usual chocolate, strawberry, or vanilla. But the treat wasn’t really magical until 1974. It was during this time that Philadelphia Eagles player Fred Hill was reaching his breaking point of watching his then 3-year-old daughter undergo leukemia treatment while basically living at St. Christopher’s Hospital for Children. He thought that there must be a better way to care for children like his daughter. The Eagles’ general manager reached out to the local McDonald’s ad agency who agreed to promote a St. Patrick’s Day Green Milkshake promotion where the proceeds from the holiday drink would go toward purchasing a house near the hospital where families could care for their sick children in a more comfortable environment. The house became the first Ronald McDonald House. Today there are 322 Ronald McDonald Houses in 57 countries and regions. And the tradition continues on! This year, for every Shamrock Shake that is sold from March 11-17, 25 cents will be donated toward the Ronald McDonald House Charities.

As popular as the Shamrock shakes are, it wasn’t until 2012 that McDonald’s finally offered the beverage at every one of their locations. It might be just as well that they are only available for a limited time. One large Shamrock Shake (22 ounces) contains 820 calories, but if that doesn’t matter to you and you still want one when they start running scarce, you can always visit shamrockshake.com to find out where they are hiding.

In addition to the Shamrock Shake, you might be surprised to learn that another menu item is a hot seller during March as well. Though McDonald’s Filet-O-Fish sandwiches are available year round, sales of the fishwich skyrocket during the month of March. Why? In addition to St. Patrick’s Day, March is also the season of Lent which begins on March 1. It is during this time that many Catholics avoid meat on Fridays. According to MSN, the burger chain sells about 25 percent of their Filet-O-Fish sandwiches during this time of the year.

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Catholics owe some thanks to Lou Groen for the meat-alternative sandwich. Groen owned the first McDonald’s in Cincinnati, Ohio, who noticed that his burger stand became almost empty on Fridays and suggested to Ray Kroc a new recipe that he had created using white Pollock fish. As it turns out, Kroc was already coming up with a meat-alternative sandwich recipe of his own that he proudly called the Hula Burger which was essentially a grilled pineapple slice and a slice of cheese on a bun.

If you’ve seen Michael Keaton’s portrayal of Kroc in the movie The Founder, you know that he wasn’t a man who gave up on his ideas easily. One Friday, Kroc challenged Groen to see who could sell more of their own sandwiches. At the end of the day, Groen sold 350 Filet-O-Fish sandwiches but Kroc only sold six of his Hula Burgers.

[Featured Image by Gene J. Puskar/AP Images]