Whisk together the dry ingredients in a medium/large mixing bowl. Stir through the cubed butter just to distribute and drizzle in the oil.
Add the sweet potato puree to the bowl but keep it in a small spot to the side of the bowl.
Pour 150g of the boiling water over the flour, not the sweet potato. We want to scald the flour which creates elasticity and allows the dough to absorb more water than it otherwise would.
Stir everything together (sweet potato puree included) then get your hands into the bowl and squelch the dough through your fingers. The butter should melt in as you work. Your ideal consistency is a light orange dough that is juicy, moist and elastic feeling with no flour in the bowl and no crumbly texture. You should easily be able to pick it up and shape it into a ball, but it should not feel even a tiny bit dry. Add the water in increments until you reach this consistency.
Divide the dough into 6 large balls and keep the remainder covered (I place them on the bench and invert the mixing bowl over the top).
Flour a clean bench space lightly but thoroughly with tapioca flour.
Take the first ball and place it on the floured work surface. Use a rolling pin to roll it out to a little larger than your 25cm (10 inch) bowl lip or springform pan ring. This will be your cutter to cut each tortilla out.
Take your time to roll the dough to an approximate 3-5mm width – it should be very thin. A chunky and thick tortilla will not bend nicely and won't taste as good. Take the time to do it right – I promise the results are worth it and I promise the dough can easily be rolled this thin. If yours can't and feels too stiff, dry or fragile, stop and add more boiling water, taking care to knead it in thoroughly. Dough that is too dry feels hard to work with but properly hydrated dough is nice and flexible.
Use the cutter to cut the tortilla. Pull off the dough around the edges or use a knife if it is not cut clean off the tortilla. Repeat with the remaining dough and tortillas, incorporating the scraps into another ball of dough as you work. You should might get 7-8 tortillas with this volume of dough.
Thoroughly preheat a large skillet over a medium heat. The skillet really needs to be larger than the circumference of the tortillas so that it can lie flat as it cooks. This allows the edges to cook evenly with the centre of the tortilla.
Once the skillet is thoroughly heated add a scant amount of oil. Place the first tortilla down. Give the top of the tortilla a little drizzle of oil and brush it evenly across the tortilla with a pastry brush.
Cook the tortilla for a couple of minutes, depending on how high your heat is. Flip the tortilla and cook for half the time on the second side. We don't want to overcook the tortilla as it can easily become too dry and stiff, so don't leave it for too long on the second side. I like to aim for a tortilla with golden spots but only just cooked through, so adjust your heat as necessary.
If your tortilla gets stuck, stop and allow the pan to heat for longer before continuing.
Transfer each tortilla to a clean dry tea towel and keep them covered as you work. The steam helps keep them supple and flexible. Repeat with the remaining tortillas.
Allow the tortillas to cool completely before transferring them to an airtight container or the freezer. I like to put a sheet of baking paper between each tortilla and freeze them. This way I can use one at a time and they don't get stuck together after freezing.
After a few days in the fridge, you can soften the tortillas by microwaving or steam heating them before use.