To a large mixing bowl, add cassava flour, buckwheat flour and salt. Stir to combine.
Next, add boiling water and olive oil and using a wooden spoon or fork, stir to combine - being careful not to burn yourself.
Once cool enough to touch, begin kneading the dough until a soft, pliable dough ball forms, adding more water or flour as needed (1 Tbsp at a time). You want the dough to be soft and moist but not sticky.
Heat a well-seasoned, heavy-bottomed cast iron pan over medium-high heat.
Cut dough ball into 4 equal pieces and store the ones you're not using under a dish towel or piece of plastic wrap to prevent them from drying.
Roll one of your dough portions into a ball and using a tortilla press, heavy pan or rolling pin, roll dough out to about 1/4 inch thickness.
Once pan is hot place tortilla in pan and cook until large bubbles begin to form inside of it.
Flip the tortilla and continue cooking until a large bubble forms again. Remove from pan and set aside on a plate covered with a clean dish towel.
Continue this process for the remaining pieces of dough, being careful to adjust the heat of the pan, reducing if necessary. You may also need to add a little oil (I recommend avocado oil for this) if using a cast iron pan.