Beat 1 1/4 cups dark brown sugar and 1 stick butter until fluffy, then beat in 1 egg and 1 teaspoon vanilla. Whisk 1 1/2 cups flour, 1/2 cup Dutch-process cocoa powder, 3/4 teaspoon salt and 3/4 teaspoon baking soda; stir into the butter mixture. Chill 30 minutes, then roll into balls and bake 12 to 15 minutes at 350 degrees. Roll finished cookies in confectioners' sugar.
Recipe courtesy Food Network Magazine