Preheat oven to 350 degrees.
Blend cookie crumbs and butter in small bowl.
Sprinkle 1 cup crumb mixture over bottom of lightly greased 9 x 9 inch baking pan.
Sprinkle with white chocolate chips, marshmallows and walnuts.
Top with remaining crumbs.
Pour condensed milk evenly over crumbs.
Bake for 30 minutes.
Cool completely in pan.
Cut into bars. Store in airtight container.