This butternut squash Italian sausage and turnip green gratin is a comforting and flavorful dish that is perfect for fall. The butternut squash is roasted until tender, then layered with Italian sausage, turnip greens, and a creamy cheese sauce. The gratin is baked until golden and bubbly, creating a delicious and satisfying casserole. Serve it as a main dish or as a side dish with roasted chicken or turkey.