Preheat oven to 350 degrees F. Butter or grease a 13- by 9-inch baking pan.
In a large bowl, beat butter until creamy. Beat in flour and brown sugar until well mixed. With floured fingers, press 1 ¾ cups crumb mixture onto bottom of prepared baking pan; reserve remaining mixture. Bake approximately 10 to 12 minutes or until edges are golden brown; remove from oven and set aside.
1 cup butter, 2 cups flour, ½ cup firmly-packed light brown sugar
In a small saucepan over low heat, combine ½ cup semisweet chocolate chips, ½ cup bittersweet chocolate chips, and sweetened condensed milk. Melt over low heat, stirring until smooth. Remove from heat and spread over prepared hot crust.
1 cup semi-sweet chocolate chips, 1 cup dark, 1 14-ounce can sweetened condensed milk
Stir chopped nuts into reserved crumb mixture; sprinkle over chocolate filling. Drop, by teaspoons, raspberry jam over the crumb mixture. Sprinkle with remaining 1 cup semisweet and bittersweet chocolate chips.
1 cup semi-sweet chocolate chips, ½ cup walnuts chopped, ⅓ cup seedless raspberry jam, 1 cup dark
Return to oven and continue baking for 25 to 30 minutes or until center is set. Remove from oven and let cool in the pan on a wire cooling rack. Once cool, cut into bars.