1 cup all-purpose flour
¼ cup non-alkalized cocoa powder
½ tsp baking soda
⅛ tsp salt
1¾ tsp instant espresso powder
1½ tsp vanilla extract
½ cup unsalted butter, softened
½ cup granulated sugar
½ cup firmly packed dark brown sugar
1 large egg, at room temperature
Espresso Ganache Filling
5 oz bittersweet chocolate, coarsely chopped
⅓ cup heavy cream
½ tsp instant espresso powder
Make the cookies:
Position two racks near the centre of the oven and preheat the oven to 350ºF.
In medium bowl, whisk together the flour, cocoa powder, baking soda and salt until thoroughly blended.
In a small cup, combine the espresso powder and vanilla extract and stir with a small rubber spatula until the espresso powder is dissolved.
In the bowl of an electric mixer, using the paddle attachment, beat the butter at medium speed until creamy, about 30 seconds. Add both sugars and continue beating until the mixture is light in texture and colour, 2 to 3 minutes. Scrape down the sides of the bowl. Beat in the egg until well blended. Beat in the espresso mixture. At low speed, beat in the flour mixture in three additions, scraping down the sides of the bowl after each addition.
Drop the dough by slightly rounded teaspoonfuls onto greased baking sheets, leaving about 1½ inches between them. Bake, two sheets at a time, for 7 to 9 minutes, until the edges of the cookies are very lightly browned but the centres are still slightly soft, switch the positions of the baking sheets halfway through the baking time for even browning. (For crisp cookies, bake for 8 to 10 minutes, until the centres are no longer soft.)
Cool the cookies on the baking sheets on a wire rack for 1 to 2 minutes, then, using a metal spatula, transfer the cookies to the rack to cool completely.
Make the filling:
Place the chocolate in the bowl of a food processor and process until finely chopped. In a small saucepan, combine the cream and espresso powder and bring to a boil, stirring to dissolve the espresso powder. With the motor running, add the hot cream mixture to the chopped chocolate and process for 25 to 30 seconds, or until completely smooth, stopping to scrape down the sides of the bowl once or twice if necessary.
Scrape the ganache into a medium bowl. Let stand at room temperature until just slightly set and spreadable, about 30 minutes.
Assemble the cookies
Spread a gently rounded teaspoonful of the ganache filling onto the bottom of half the cookies. Top with the remaining cookies, right side up, and very gently press each sandwich together. Let sit at room temperature for about 30 minutes to set the ganache.
Store in an airtight container at room temperature for up to 3 days. Makes about 32 sandwich cookies.
Instant coffee powder can be used in place of the espresso powder, but the flavour will not be as intense.
Source: The Good Cookie, 2002