Unless you live in the Northeast, you may not have heard of Whoopie Pies. An interesting name, I realize, possibly conjuring up all kinds of odd images about what they are. It is not known for sure how the name originated, but three states claim ownership of the tasty treat: Pennsylvania (from the Amish culture there), Massachusetts  (the Berwick Cake Company of Boston), and Maine (the Lebadies Bakery). Since I grew up thinking they were strictly an Amish tradition, I am going to share their version of the story. Their explanation is that one day an enterprising cook baked some leftover cake batter into large individual circles. Once baked, a creamy filling was added and Amish women started including them in the lunch pails of their husbands and children. When the lucky recipients found one in their lunch they would shout "whoopie!" Sounds to me like as good an explanation as any. 
So what are Whoopie Pies really? Well, they actually aren't a "pie" at all, rather they look like a huge Oreo (or in the case of the ones I made - a Chipwich), but with a softer texture: deliciously fluffy, creamy filling sandwiched between two rich cake-like rounds. Traditionally, the cake part was chocolate, and the filling was a frosty white - this is still the most common, but now many versions exist, including pumpkin, peanut butter, molasses, and chocolate chip, as in this recipe I found on a package of Whole Foods mini chocolate chips. They are sinfully decadent, so cutting one in half might be enough to satisfy. Also, I ended up refrigerating mine to keep them from spoiling; I'm sure they could be frozen too. I really liked them right out of the fridge, but you could also bring them to room temperature before eating.

Chocolate Chip Whoopie Pies
Makes about 20 pies
Ingredients
Cakes:
3 cups all-purpose flour
2 tsp baking powder
1 tsp fine sea salt
10 tbsp unsalted butter, softened
1 cup sugar
2 large eggs
1 tbsp vanilla
2/3 cup buttermilk
2 1/2 cups mini semi-sweet chocolate chips, divided
Filling:
1/4 cup (1/2 stick unsalted butter, softened
3 cups confectioners sugar
6 ounces cream cheese, softened 
1/4 tsp fine sea salt

Directions
Preheat oven to 375. To make cakes, whisk together flour, baking powder and salt in a large bowl. In a separate bowl, beat butter and sugar with an electric mixer for about 1 minute. Add eggs and vanilla and beat again until well combined. Blend in half the flour mixture and then half the buttermilk. Repeat with remaining flour mixture and buttermilk and then stir in half the chocolate chips. 
Working in batches, drop 2 tablespoons of the dough onto a large, parchment-paper lined cookie sheet to form each cake, spacing about 2 in apart. Dip fingertips in water to prevent sticking and shape and smooth the cakes into flat, 2 in circles. Bake until puffed and golden brown on the bottom, about 10 minutes. Set aside to cool.
For the filling, in a large bowl, beat butter, sugar, cream cheese until very fluffy, about 2-3 min.
Sandwich about 2 tablespoons of filling in between two cakes to make each pie, pressing together gently. Transfer remaining 1 cup chips to a wide, shallow dish and gently roll edges of pies in the chips to coat sides. (I also used some rainbow sprinkles for some). Let set for one hour before serving. 
Source: Whole Foods

References: The Oxford Companion to American Food and Drink