Pierce a large sweet potato, set it on a foil-lined pan and roast at 425F for 45 to 55 minutes, until a knife slides through with no resistance. Roast rather than boil, since a boiled potato carries water into the dough.

Scoop out the flesh, mash it completely smooth with no lumps, and cool it to room temperature. Measure out 1 cup, about 240g.

Combine the cooled mashed sweet potato with 1 cup of the flour, and the salt if using. Mix with a fork until it forms a shaggy mass.

Turn onto a lightly floured counter and knead 2 to 3 minutes, adding the remaining flour a tablespoon at a time only as needed. The dough should be soft and smooth, slightly tacky to the fingertip, holding a thumbprint and pulling cleanly off the bowl.

If it smears and strings on your palm, add flour a tablespoon at a time. If it cracks at the edges, add a teaspoon of mashed potato rather than water.

Rest the ball under the upturned bowl for 10 minutes so it relaxes and rolls easily.

Divide the dough into 6 equal pieces and roll each into a ball. Roll each ball between two sheets of parchment to about ⅛ inch thick and roughly 7 inches across. Roll them all before you start cooking.

Heat a cast iron or heavy nonstick skillet over medium-high heat with no oil. Peel off the top parchment and lay one round in the dry pan.

Cook 60 to 90 seconds per side, until dark freckled blisters appear and the surface turns from wet-looking to matte. The center stays pale and soft. Do not cook past this or they turn crisp.

Stack each tortilla on a plate under a clean kitchen towel the moment it leaves the pan. They steam each other soft as they rest. Repeat with the remaining rounds.