Preheat oven to 350F. melt butterscotch morsels and butter together and blend till smooth. Stir in graham cracker crumbs and nuts and mix till small crumbs form. Reserve 2 cups crumb mixture for topping. Press rest of mixture into ungreased 13x10inch baking pan. Bake 12 minutes.
Meanwhile, combine softened cream cheese and sugar in large bowl. Beat until creamy. Add eggs 1 at a time beating well after each addition. Blend in flour and lemon juice. Pour evenly over hot baked crust. Sprinkle top with reserved crumb mixture.
return to oven and bake 25 minutes.