Combine all the ingredients except the boiling water in a mixing bowl and whisk to incorporate.
Add the boiling water, starting with 1/2 cup (125ml). Stir quickly and add more water as necessary. The dough should be slightly sticky and moist with no dry flour on the bottom.
Once it is cool enough to handle, knead the dough into a smooth ball and cover. Leave for 5-10 minutes.
Liberally flour a clean, dry bench top with tapioca flour. Divide the dough into four tortillas. The offcuts from each will form the fifth tortilla, so set those aside as you work.
Roll each tortilla to your desired width (about 2-3mm – any thicker and they become too chewy). Use a large circular cutter or the lip of a circular bowl to cut each tortilla into a round. Set them aside without touching each other, and finish by gathering all the offcuts for the last tortilla.
Preheat a pan to a high heat for 2-3 minutes. Add a splash of vegetable oil to the pan once hot, and cook the first tortilla. Cook for a minute or so before flipping (this will depend on how hot your pan is). Flip and cook on the other side, before transferring to a cooling rack. Repeat with the remaining tortillas.
Serve warm or store in an airtight container. The tortillas are best fresh, but reheating them in the microwave or a steamy oven will restore their flexibility.
Notes
There is no alternative for cassava flour in this recipe. See the recipe in my cookbook, Intolerance Friendly Kitchen, for a grain based recipe without cassava flour.
Cassava flour is distinctly different from tapioca flour or tapioca starch. They are not interchangeable in this recipe.
The butter can be melted or softened. It will melt in the boiling water either way.