Garlic Parmesan Mashed Potato Casserole makes the PERFECT Thanksgiving and holiday side dish! Creamy russet potatoes are cooked with garlic cloves, then mashed with butter, milk and Parmesan cheese. Top with additional Parmesan before baking to create a crispy exterior on this comforting casserole. No matter if you’re serving the family for a holiday or on a weeknight, Mashed Potato Casserole packs a flavorful punch for any meal! Side Dishes