To make these Dark Chocolate Banana Muffins gluten-free, replace the all-purpose flour with a certified gluten-free 1:1 baking flour blend suitable for muffins. Confirm that the chocolate baking bar, mini chocolate chips, espresso powder, vanilla extract, baking soda, sugar, sour cream, butter, egg, salt, and bananas are gluten-free and free from cross-contact warnings. Some chocolate products and espresso powders may be processed on shared equipment, so check labels carefully. Use clean mixing bowls, muffin tins, liners, spatulas, measuring tools, and cooling racks to prevent gluten contamination.