Preheat oven to 350 degrees F. In a buttered, 4 quart Pyrex souffle dish layer 2 cups turkey stuffing, making sure to pack it down and leaving a well in the center. Fill the well with cranberry sauce. Layer the turkey, onions, and remaining stuffing evenly, leaving few gaps. Pipe rosettes of alternating mashed potatoes that cover the top. Bake, uncovered, for approximately 1/2 hour or until the top is crusted and brown and the filling is warmed through. Serve hot.