To make the crust: Grease
a 13 by 9-inch metal baking pan, then line with foil, leaving a 2-inch overhang on both ends, and grease foil.
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.
chills, put oven rack in middle position and preheat oven to 375 degrees F.
Bake until golden brown, about 30 minutes. Cool crust in pan on a rack 20 minutes. (Leave oven on.)
To make brownie filling while crust cools: 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
Spread brownie batter
over cooled crust and bake until set, about 20 minutes. Cool completely in pan on rack, about 1 1/2 hours.
Run a heavy knife under hot water and wipe dry, then cut confection
into 1-inch squares. Brownie squares keep, layered between sheets of waxed paper or parchment, in an airtight container at room temperature 1 week.