Lightly spoon flours into dry measuring cups; level with a knife. Combine flours, potato, butter, salt, and cinnamon in a large bowl; mix well. Add water; press mixture together with hands. Turn dough out onto a lightly floured surface; knead until smooth (about 2 minutes).
Divide dough into 16 equal portions, shaping each into a ball. Working with 1 ball at a time (cover remaining dough to prevent drying), roll each into a 4-inch circle on a lightly floured surface (circles will be very thin).
Heat a medium cast-iron skillet over medium-high heat until very hot. Place 1 dough round in pan, and cook 2 minutes or until brown spots appear, turning after 1 minute. Place the bread on a cooking rack over the eye of a gas burner. Hold bread over flame with tongs, turning until both sides of bread are puffed and brown spots appear. (Some chapatis will puff more than others). Repeat procedure with remaining dough.