In a small bowl, combine the walnuts, brown sugar, flour, and shortening. Mix with a fork or pastry blender until the mixture resembles coarse crumbs.
Sprinkle the streusel evenly over the cranberry filling.
Set the pie on a baking sheet and bake for 55 to 60 minutes, until the crust is golden and the filling is bubbling. Tent the edges with foil if they brown too quickly.
Cool completely before slicing and serving.