To create a version of a Boston Cream Pie you can simply replace the regular flour in the sponge cake with a gluten-free flour blend that can be used in equal amounts. It's important to pick a blend that holds xanthan gum. To maintain the cake's desired texture. The cornstarch used in the pastry cream is naturally gluten-free so you won't need to make any adjustments! Just make sure that the chocolate you use for the ganache is labeled as gluten-free to avoid any traces of gluten.