Melt 2 Tbsp. butter in a large skillet over medium-high heat; add onion, bell pepper, and celery blend, and sauté 8 minutes or until tender. Combine sautéed vegetables, cornbread, turkey, and next 3 ingredients in a large bowl. Toss gently. Spoon mixture into a lightly greased 11" x 7" baking dish. Cover to keep warm.
Meanwhile, heat potatoes in microwave according to package directions. Stir in remaining 1 Tbsp. butter. Spread 1 cup cranberry sauce over turkey mixture. Top with potatoes. Bake, uncovered, at 375° for 15 minutes or until thoroughly heated.