Yields 48 sandwich cookies (serving size: 1 sandwich cookie)
Photo: Oxmoor House
1 3/4 cups all-purpose flour
3/4 cup sugar
2/3 cup unsweetened dark cocoa powder
1/2 teaspoon baking soda
1/4 teaspoon salt
12 tablespoons (1 1/2 sticks) unsalted butter, cut into small pieces
1 large egg white
1/3 cup vegetable shortening, at room temperature
5 1/2 tablespoons unsalted butter, at room temperature
1 2/3 cups confectioners' sugar
1 teaspoon vanilla extract
How to Make It
Make cookies: In a large bowl, using an electric mixer on low speed, beat together flour, sugar, cocoa powder, baking soda, salt and butter until crumbly. Add egg white and 1 Tbsp. water; beat until blended.
Divide dough in half. Roll each piece into an 8 1/2-by-1 1/2-inch log. Wrap in plastic wrap; chill for 2 hours.
Line 2 baking sheets with parchment. Place racks in upper and lower thirds of oven and preheat to 350°F. Cut each log into 48 slices (about 1/8 inch thick). Place on lined sheets, about 2 inches apart.
Bake until cookies are set, 10 to 12 minutes, rotating sheets once. Let cookies cool on sheets on wire racks for 2 minutes, then transfer to wire racks to cool completely.
Make filling: In a medium bowl, using an electric mixer on medium speed, beat together shortening and butter until smooth. Gradually add sugar, beating on low speed until blended. Beat in vanilla.
Spread 1 1/2 tsp. filling onto flat side of 48 cookies; top with remaining 48 cookies, flat side down.