To make this Spanish Bar Sheet Cake gluten-free, replace the all-purpose flour with a certified gluten-free 1:1 baking flour blend. Confirm that the baking soda, spices, raisins, caramel sauce, shortening or butter, sugar, and all packaged ingredients are certified gluten-free or labeled free from gluten-containing additives. Some caramel sauces, spice blends, and dried fruits may have cross-contact risks, so check labels carefully. Use clean mixing bowls, measuring tools, utensils, pans, and prep surfaces to prevent gluten contamination.