Gratin is a type of casserole dish that is typically made with ingredients such as cheese, bread, and vegetables. The dish is covered with breadcrumbs and baked until crispy and golden brown on top. A sandwich can be made by sandwiching fillings between two slices of bread, and the fillings can be chosen based on personal preference. Gratin sandwich refers to a variation of the traditional gratin dish where the ingredients are used to make a sandwich. The 26Pcs indicates that there are 26 pieces of the Gratin sandwich in total.