1. Pick a cookie flavor.
VANILLA: Whisk 2 3/4 cups flour, 1 teaspoon baking soda and 3/4 teaspoon each baking powder and salt in a bowl. In a separate bowl, beat 1 stick softened butter, 1 1/3 cups granulated sugar and 2 teaspoons vanilla with a mixer on medium-high speed until fluffy; beat in 1 egg. On low speed, beat in the flour mixture in 3 batches, alternating with 2/3 cup buttermilk in 2 batches; beat until just combined.
CHOCOLATE: Whisk 2 cups flour, 2/3 cup unsweetened cocoa powder (not Dutch process) and 1 teaspoon each baking soda and salt in a bowl. In a separate bowl, beat 10 tablespoons softened butter, 1 1/4 cups light brown sugar and 1/2 teaspoon vanilla with a mixer on medium-high speed until fluffy; beat in 1 egg. On low speed, beat in the flour mixture in 3 batches, alternating with 1 cup buttermilk in 2 batches; beat until just combined.
2. Bake the cookies.
Line 3 baking sheets with parchment paper and lightly coat with cooking spray. Scoop 16 mounds of batter onto the baking sheets, about 2 inches apart (about 2 tablespoons batter per cookie); gently form into rounds with damp fingers and smooth the tops. Refrigerate until firm, about 30 minutes. Preheat the oven to 400 degrees F. Bake the cookies until they spring back when pressed, 10 to 12 minutes. Cool 5 minutes, then remove to a rack to cool completely.
3. Make the filling.
Beat 1 stick softened butter with a mixer on medium speed until fluffy; gradually beat in 1 cup confectioners' sugar. Gradually beat in 2 tablespoons milk, then another 1 cup confectioners' sugar; beat until smooth, about 3 minutes. Mix in 1/2 teaspoon vanilla. Fold in one of the following (or leave as is for vanilla filling):
*2 tablespoons seedless raspberry jam
*2 tablespoons cocoa powder dissolved in 2 tablespoons hot water
*2 1/2 tablespoons lemon curd
*1/4 cup dulce de leche or thick caramel sauce
4. Assemble the whoopie pies.
Sandwich about 2 tablespoons filling between 2 cookies; repeat with the remaining cookies and filling. Roll the edges in any of the following:
*Crushed graham crackers
*Toasted shredded coconut
*Chopped candy bars
*Mini chocolate chips
*Chopped white chocolate
Photograph by Kang Kim