Combine 2 cups flour and powdered sugar in a bowl. Cut 1 cup butter into flour mixture with a pastry blender until mixture is crumbly. Spoon flour mixture into an ungreased 13" x 9" baking dish. Press crumb mixture firmly into pan. Bake at 350° for 20 minutes or until shortbread crust is lightly browned.
Melt caramels and whipping cream in a saucepan over medium heat, stirring frequently. Remove from heat, and stir in 1/2 cup cashews. Pour over crust in pan.
Combine 1/4 cup flour, oats, brown sugar, 1/4 cup cashews, and melted butter; stir well. Dollop streusel mixture over caramel in pan, spreading slightly. Bake at 350° for 20 minutes or until edges are lightly browned. Cool completely in pan on a wire rack. Cut into bars, using a sharp knife.