The cassava flour with tapioca starch creates the best results and I don't recommend any substitutions. The use of these two ingredients keeps this recipe completely cassava based. Cassava flour comes from grinding the whole cassava root into a fine powder and is a great, gluten-free substitute for wheat flours. Tapioca starch is also made from cassava root, but exclusively from the starch which is extracted from the root and further refined into a very light and fine powder.