1Heat oven to 350ºF. Mix brown sugar, 1 cup butter, the vanilla and egg in large bowl. Stir in flour. Spread evenly in bottom of ungreased rectangular pan, 13x9x2 inches. Bake 20 to 22 minutes or until light brown. Cool 20 minutes.
2While crust is baking, heat chocolate chips, corn syrup and 2 tablespoons butter in 1 1/2-quart saucepan over low heat, stirring constantly, until chips are melted. Cool 20 minutes.
3Spread chocolate mixture over crust. Sprinkle with nuts; gently press into chocolate. Refrigerate uncovered about 2 hours or until chocolate is firm. For 48 squares, cut into 8 rows by 6 rows. Store covered in refrigerator.