Source: Martha Stewart
8 ounces bittersweet chocolate, melted and cooled
1 1/4 cups all-purpose flour
1/2 cup Dutch-process cocoa powder
2 teaspoons baking powder
1/4 teaspoon salt
8 tablespoons unsalted butter (1 stick) room temperature
1 1/3 cup light-brown sugar
2 large eggs
1 teaspoon pure vanilla extract
1/3 cup milk
1 cup confectioners' sugar
Heat oven to 350 degrees. Chop chocolate into small bits. On top of the stove, set a heatproof bowl, or the top of a double boiler, over a pan of simmering water. Melt the chocolate over medium heat. Set aside to cool. Sift together the flour, cocoa, baking powder, and salt.
In the bowl of a heavy-duty electric mixer fitted with the paddle attachment, beat the butter and light-brown sugar until light and fluffy. Add the eggs and vanilla, and beat until well combined. Add the melted chocolate. Add the dry ingredients alternately with milk. Mix on a low speed until just combined. Divide the dough into quarters, wrap with plastic wrap, and chill in the refrigerator until firm, about 2 hours.
Divide each quarter into 16 1-inch balls. Roll in confectioners' sugar, coating thoroughly. Place the cookies on a Silpat-lined baking sheet two inches apart. Bake until the cookies have flattened and the sugar splits, 12 to15 minutes.
Transfer from oven to a wire rack, and let cool completely. Store in an airtight container for up to one week.
I talked about this recipe HERE.