This is a recipe I got from Good Housekeeping a few years ago. The good thing about it is that you can make the cookies ahead, cool them completely and freeze them in an airtight container, with waxed paper between the layers. They will be good for up to a month. When needed, thaw, and add filling before serving.
2 cups all-purpose flour
2/3 cup unsweetened cocoa
1 tsp baking soda
1/4 tsp salt
2 ripe bananas
1/3 cup sour cream
1 tsp vanilla extract
6 tbsp butter or margarine, softened
1 cup sugar
1 large egg
1 1/3 cups marshmallow creme
Preheat oven to 350 degrees.
Line 2 cookie sheets with parchment paper; set aside.
In a medium bowl, whisk the flour, cocoa, baking soda, and salt together.
From the bananas, mash up 1/2 cup; finely chop the remaining and reserve.
In another medium bowl, mix the mashed banana, sour cream, and vanilla.
In a large mixer bowl, beat butter and sugar at medium-high speed until well combined. Beat in the egg until well blended, scraping bowl occasionally. Reduce speed to low. Add the flour mixture alternately with the sour cream mixture, beginning and ending with the flour mixture; beat just until batter is smooth, scraping bowl occasionally.
Drop batter onto the prepared cookie sheets 1 rounded tablespoon at a time, spaced 2-inches apart. With wet fingertips, flatten tops of balls to form rounds.
Bake 12 to 15 minutes at 350 degrees, centers will spring back when lightly pressed when cookies are done.
Rotate the sheets between upper and lower oven racks halfway through baking. Set cookie sheets on wire racks and allow cookies to cool completely.
Turn half the cookies flat side up and top each with 1 tablespoon of the marshmallow creme. Divide the chopped banana among the centers of the marshmallow creme topping. Add remaining cookies atop the creme filling to make sandwich-style.
Yield: 20 whoopie pies.