Double Chocolate Brownie Bars

Packaged fudge brownie mix makes this rich, delicious, chocolate treat, quick and simple to prepare. 1 (19.8 or 21.5 oz) package fudge brownie mix 3/4 cup chopped walnuts 2 cups semi-sweet chocolate chips 1/4 cup butter or margarine 1 (14 oz) can sweetened condensed...