Courtesy Gourmet Magazine
1⁄2 cup all-purpose flour
3⁄4 cup packed dark brown sugar
1⁄2 cup unsweetened cocoa powder (not Dutch-process)
1 large egg
1 teaspoon baking soda
1 cup semisweet chocolate chips (6 ounces)
1⁄2 teaspoon salt
1 cup coarsely crushed peppermint hard candies (1⁄4 pound)
1 stick (1⁄2 cup) unsalted butter, softened
Put oven rack in middle position and preheat oven to 375°F. Line a 13-by-9-inch metal baking pan with 1 sheet of foil, allowing 2 inches of foil to hang over each end of pan, and butter foil (except overhang).
Whisk together flour, cocoa powder, baking soda, and salt in a small bowl.
Beat together butter and brown sugar in a large bowl with an electric mixer at high speed until pale and fluffy, about 3 minutes. Beat in egg until combined.
Reduce speed to low, then mix in flour mixture until just combined. Stir in chocolate chips and candy.
Spread dough evenly in pan and bake until puffed and beginning to pull away from sides of pan, about 20 minutes.
Cool completely in pan on a rack, then, lifting with foil, transfer to a cutting board. Cut into bars and lift off foil with a spatula.