To make these Hot Cocoa Brownies gluten free, replace the all-purpose flour with a certified gluten-free 1:1 baking flour blend. Verify that the hot cocoa mix, semi-sweet chocolate chips, marshmallows, vanilla extract, baking spray, and all packaged ingredients are labeled gluten free or free from gluten-containing additives. Use clean mixing bowls, measuring cups, utensils, baking pan, and parchment paper to prevent cross-contact with gluten-containing ingredients.