These are a big deal up here in Maine.
They aren't really like a pie at all. They are a hamburger sized cake sandwich. The original ones are made with two chocolate cake circles and a generous amount of vanilla-cream filling. Some Maine bakeries make them in the shape of a mussel.
Mainers claim that Whoopie Pies started in Maine. However, many people believe that they originated with the Amish, in Lancaster county, Pennsylvania. Whoopie Pies are popular both places and quite a treat with the tourists.
Here's a recipe if you want to make your own.
Whoopie Pies:
2 c. sugar
3/4 c. shortening
2 eggs, slightly beaten
2 c. milk
2 tsp. vanilla
10 tbsp. cocoa
4 c. flour
2 1/2 tsp. soda
Pinch of salt
Filling:
1 1/2 c. shortening
1 1/2 c. confectioners sugar
12 tbsp. marshmallow fluff
2 tsp. pure vanilla
Cream shortening and sugar. Combine beaten eggs, milk and vanilla and beat into creamed mixture. Slowly stir sifted dry ingredients into the creamed mixture, and beat on medium speed about 2 minutes. Drop with tablespoon onto greased and floured cookie sheet (enough dough to make a baked cookie about 2 to 2 1/2 inches). Bake at 350 degrees until cookie just springs back when pressed in center with finger. Remove to rack and cool completely before filling.
Combine fluff, shortening, and vanilla and beat until well mixed. Slowly add confectioners sugar until well mixed. Place a generous amount on the flat side of one cookie and top with another cookie. Makes about 2 dozen whoopie pies.