To make these Snickerdoodle Cupcakes gluten free, replace the all-purpose flour and cake flour with a gluten-free 1:1 baking flour blend that contains xanthan gum. Use certified gluten-free baking powder, vanilla extract, cinnamon, and snickerdoodle cookies. If preparing homemade snickerdoodle cookies for the topping, make them with gluten-free flour as well. Always check frosting ingredients and package labels to avoid hidden gluten or cross-contamination.