Active time: 1 hr Start to finish: 3 3/4 hr (includes cooling)

　　

Ingredients

Makes about 6 dozen cookies

　　

For crust

Ingredients for basic butter cookies

　　

For brownie filling

1 1/2 sticks (3/4 cup) unsalted butter

　　10 1/2 oz fine-quality bittersweet chocolate (not unsweetened), chopped

　　1 1/2 cups packed light brown sugar

　　3 large eggs, lightly beaten

　　1 1/4 teaspoons vanilla

　　3/4 cup all-purpose flour

　　1/4 cup plus 2 tablespoons Dutch-process unsweetened cocoa powder

　　3/4 teaspoon salt

　　1 1/2 cups walnuts (6 oz; optional), toasted , cooled, and coarsely chopped

　　

Make crust:

Step 1

Grease a 13- by 9-inch metal baking pan, then line with foil, leaving a 2-inch overhang on both ends, and grease foil.

　　

Step 2

Follow recipe for basic butter cookies to make dough (do not chill), then press dough evenly onto bottom of baking pan, using plastic wrap on top to prevent dough from sticking to your fingers, and chill until firm, about 20 minutes.

　　

Step 3

While crust chills, put oven rack in middle position and preheat oven to 375°F.

　　

Step 4

Bake until golden brown, about 30 minutes. Cool crust in pan on a rack 20 minutes. (Leave oven on.)

　　

Make brownie filling while crust cools:

Step 5

Melt butter and chocolate with brown sugar in a 3-quart heavy saucepan over moderate heat, stirring occasionally, until smooth. Remove from heat, then whisk in eggs and vanilla until combined well. Whisk in flour, cocoa, and salt, then stir in walnuts (if using).

　　

Step 6

Spread brownie batter over cooled crust and bake until set, about 20 minutes. Cool completely in pan on rack, about 1 1/2 hours.

　　

Step 7

Run a heavy knife under hot water and wipe dry, then cut confection into 1-inch squares.

　　Cooks' note:

　　Squares keep, layered between sheets of wax paper or parchment, in an airtight container at room temperature 1 week.