To make this Ham and Cheese Sandwich gluten-free, replace the seeded wholegrain bread or baguette with certified gluten-free bread. Confirm that the deli ham, cheese, Dijon mustard, mayonnaise, butter, and any optional tomato or add-ins are labeled gluten-free and free from cross-contact warnings. Use clean utensils, cutting boards, knives, and serving plates to prevent gluten contamination.