PREHEAT oven to 350° F.
MICROWAVE morsels and butter in medium, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. Morsels may retain some of their original shape. If necessary, microwave at additional 10 to 15-second intervals, stirring just until morsels are melted. Stir in crumbs and nuts. Reserve 2 cups crumb mixture; press remaining mixture into ungreased 15 x 10-inch jelly-roll pan.
BAKE for 12 minutes.
BEAT cream cheese and sugar in large mixer bowl until creamy. Add eggs one at a time, beating well after each addition. Beat in flour and lemon juice. Pour over crust; sprinkle with reserved crumb mixture.
BAKE for 20 to 25 minutes or until set. Cool in pan on wire rack. Cut into bars or diamonds; refrigerate.