Preheat the oven to 375ºF. In a bowl, combine the turkey, 1 cup of the cheese, celery, cranberries, mayonnaise, mustard, and black pepper. Mix well. Set aside.
Unroll the 2 packages of crescent rolls. With the wide end of the triangles toward the center, arrange 8 triangles in a circle on a pizza pan/stone. Next, form an inner circle of dough by matching the wide ends of the remaining 8 triangles to the wide end of each outer triangle. Press the seams together with fingers.
Scoop the filling over the dough, around in a wreath shape.
Beginning with the last triangle placed in the center of pizza pan, bring the point of the triangle straight across the filling. Next, bring the point of the opposite outside triangle diagonally across the filling, covering the point of the previous triangle. Continue to overlap crescent triangles by tucking the points under the wreath.
Brush the top of the wreath with the egg white (it helps give it a glossy color and extra crispness), and bake 25 to 30 minutes or until golden brown.