In a medium mixing bowl, combine cassava flour, tapioca starch, xanthan gum, and salt. Add hot water and melted butter (or other fat) and stir to combine into a shaggy dough. Use your hands to knead into a smooth dough. The dough may seem sticky at first, but will become smooth and not-tacky after 30 seconds or so of kneading as the cassava soaks up the moisture. The texture of your dough should be similar to very soft playdough. If it's too firm, add a few drops of water and work it into the dough. If it's too sticky, dust just in a bit more cassava flour (I've never had this happen).

Divide into 9 balls, about 49g each, and gently flatten each ball into a disk with your hand so it's no more than an inch thick. I recommend placing the dough balls under a damp towel so they don't dry out as you roll each one. If you notice a dough ball seems a bit crackly or dry after sitting, just knead in a couple of drops of water to soften it back up.

Roll out the tortillas. If using a tortilla press (my recommendation), place a square of parchment paper on the press (no larger than the press itself), then top with a dough disk and another square of parchment paper. Press the dough into a flat round circle. Peel off the top piece of parchment paper and set the tortilla aside on the bottom parchment paper. Repeat, until you have a stack of tortillas with parchment paper between. If rolling the tortillas out by hand, place a dough disk between two pieces of parchment paper. Start by using a flat baking sheet to press the tortilla as flat as possible then use a rolling pin to roll it even thinner (or roll using just a rolling pin to start, but your tortilla may not be perfectly round). It should be very thin, but not translucent (and if you mess one up, just roll it back into a ball and do it again!). You can freeze the tortillas at this point, or cook them for easy fridge storage (see notes about storage).

Preheat a cast-iron or non-stick skillet over medium-high heat until hot (I like to do two pans side by side to make this go quicker). Carefully peel a tortilla from the parchment paper. To easily peel the tortilla off the bottom parchment, I flip it over so the tortilla is upside down on my left open palm and then carefully peel off the parchment. Place the tortilla in the hot skillet and cook until it starts to bubble up with a few larger bubbles (½-1 inch), about 45 seconds. Carefully flip the tortilla and continue cooking until it puffs up, about 45 seconds (see picture). Flip and cook the tortilla until the bubbles are golden brown on both sides, less than a minute. If you notice the bubbles burning too quickly before the tortilla puffs up, adjust the heat on your burner a little lower. If you notice your tortillas taking a lot longer to cook, increase the heat. Repeat with remaining tortillas. Tip: I usually have two skillets going with tortillas side by side.

Transfer each tortilla to a tortilla warmer or a plate covered in a couple of layers of clean kitchen towels to keep them soft and warm. Serve warm.