Pie a la mode is simply a slice of pie with a scoop of ice cream on top. It originated in New York in the late 1890s when according to the legend, a gentleman named Professor Charles Watson Townsend was eating a piece of apple pie with vanilla ice cream. A woman at a nearby table inquired what his dessert was called and when he informed her that it had no name, she dubbed it pie a la mode. It has been a dessert favorite ever since and in well over 100 years since it first originated, pie a la mode hasn't changed much.
The most common type of pie a la mode is a piece of apple pie topped with vanilla ice cream. Although this is the most common way of serving it, there are other variations. The apple pie can easily be substituted for any other fruit pie such as peach pie, cherry pie, blueberry pie or strawberry rhubarb pie. Other modifications include replacing the pie with apple crumble or apple crisp. Although apple is the most common, any fruit crumble or fruit crisp can be served a la mode.
Another adaption of the classic can be done by swapping out the vanilla ice cream for another flavor such as chocolate, peach or strawberry. It doesn't matter if the ice cream is served on the top of the pie or along side of it as long as it is on the same plate. Other toppings such as whipped topping or whip cream are often served with pie, however this is not considered to be a classic pie a la mode. Basically, for it to be considered pie a la mode, the dessert must consist of a pie or pie-like base and be topped with ice cream.
One way many people and establishments serve pie a la mode is by warming up the pie before adding the ice cream. When the ice cream is added to the warm pie it begins to melt. Whether or not the pie is heated is a personal preference.
In more recent years, other variations of the dessert have been created. One of the most notable spins on the classic is the brownie sundae. Similar to pie a la mode, a brownie sundae begins with a chocolate brownie which is then topped with vanilla ice cream. One difference, other than the base of the dessert being a brownie over pie, is that the ice cream is sometimes topped with chocolate syrup, sprinkles, whip cream and a cherry.