Chocolate Sandwich Cookies

Preparation

1. Step 1

   In a large bowl, sift together the flour, cocoa, baking powder, and salt. Set aside.

   Step 2

   Cream the butter and sugar until soft and creamy in the bowl of an electric mixer fitted with the paddle attachment. Beat in the egg and vanilla.

   Step 3

   Add the flour mixture, and mix on low speed until combined. Divide the dough in half; wrap each half in plastic wrap. Chill at least 1 hour.

   Step 4

   Preheat the oven to 325°F. On a lightly floured surface, roll the dough to 1/8 inch thick. Cut into 1 1/2-inch squares using a cookie cutter. Transfer to parchment-paper–lined baking sheets, and refrigerate until firm, about 30 minutes. Gather any scraps, wrap them in plastic wrap, and chill for 30 minutes before rerolling and cutting into squares. Bake until the edges just begin to brown, about 12 minutes. Transfer to wire racks to cool.

   Step 5

   To make the white chocolate ganache, bring the cream to a boil in a small saucepan. Remove from heat, and add 9 ounces white chocolate. Let stand for 5 minutes, covered. Transfer the mixture to a medium bowl, and stir until completely smooth. Place in the refrigerator, and chill until thick enough to spread, about 1 hour, stirring every 10 minutes. Use an offset spatula to spread the ganache on half the cookies; top with the remaining cookies.

   Step 6

   Melt the remaining 3 ounces white chocolate in a small heatproof bowl set over a pan of simmering water. Make a small cone out of parchment paper, or fit a small pastry bag with a coupler and #2 Ateco tip. Fill, and decorate as desired.