Chocolate Crumb Bars

1 c. butter or margarine, softened
1/4 tsp. salt
1/2 c. granulated sugar
1 3/4 c. all-purpose flour
2 c. (12 oz. pkg) chocolate chips, divided
1 (14 oz.) can sweetened condensed milk
1 tsp. vanilla extract
1 c. chopped walnuts, opt.

Beat butter in large mixing bowl until creamy. Beat in flour, sugar and salt until crumbly. With floured fingers press two cups of the crumb mixture onto bottom of greased 13-inch by 9-inch baking pan; reserve remaining mixture. Bake in preheated 350° oven 10-12 minutes or until edges are golden brown. Combine one cup chips and milk in small, heavy-duty saucepan. Warm over low heat, stirring until smooth. Stir in vanilla. Spread over hot crust. Stir nuts and remaining chips into reserved crumb mixture; sprinkle over chocolate filling. Bake for 25-30 minutes or until center is set. Cool in pan on wire rack. Makes 30 bars.