For the cookies:
- 1 1/4 cups all-purpose flour
- 1/2 cup unsweetened Dutch-process cocoa powder
- 1 teaspoon baking soda
- 1/4 teaspoon baking powder
- 1/4 teaspoon salt
- 1 cup granulated sugar
- 1/2 cup plus 2 tablespoons (1 1/4 sticks) unsalted butter, at room temperature
- 1 large egg
For the filling:
- 1/2 cup (1 stick) unsalted butter, at room temperature
- 2 cups sifted confectioners' sugar
- 2 teaspoons pure vanilla extract
To make the cookies:
Set two racks in the middle of the oven. Preheat to 375 degrees.
In a food processor or in the bowl of an electric mixer, combine flour, cocoa, baking soda, baking powder, salt, and sugar. While pulsing, or on low speed, add the butter, then add the egg. Continue processing, or mixing, until the dough comes together in a mass.
Take rounded teaspoons of batter and place on parchment-lined baking sheets approximately 2 inches apart. With moistened hands, slightly flatten the dough. Bake for 9 minutes, rotating once to ensure even baking. Set baking sheets on a rack to cool.
To make the filling:
Place butter and vanilla in a mixing bowl and beat with an electric mixer on low speed. Gradually add the sugar. Turn the mixer on high and beat for 2-3 minutes until filling is light and fluffy.
Using a pastry bag or spatula, drop a teaspoon-size blob of filling into the center of one cookie. Place another cookie, equal in size to the first, on top of the cream. Lightly press down to work the filling evenly towards the outside of the cookie. Repeat with remaining cookies and filling.