Day 1: Make Dough & Let Rise

1. Boil potatoes until tender, reserving cooking liquid. Cool both to room temperature (alternatively, you can use leftover mashed or cooked potatoes). Bring all remaining ingredients to room temperature
2. In a mixer with the paddle attachment, mix flour, sugar and yeast together on low speed, 1 minute
3. Add salt and mix on low speed, 1 minute
4. For best results, pass the mashed or boiled potatoes through a ricer, then add to flour mixture with the butter. Mix until the dough resembles coarse meal, about 5 minutes
5. Mix the egg and potato water (or tap water) together and add to the rest of the ingredients.  Mix on low speed until the dry bits are incorporated, being careful not to overmix 
6. Transfer dough to a bowl coated with nonstick spray. Cover and allow to rise for one hour at room temperature
7. Transfer to refrigerator and chill overnight

Day 2: Roll, Rise & Bake

1. Turn dough out onto a lightly floured surface. Divide dough into 12 portions
2. Roll into balls with the palms of your hands, then use a flour-coated rolling pin to flatten into discs about 5" in diameter. Coat baking sheets with nonstick spray and place flatbreads, spaced a few inches apart
3. Cover with a clean kitchen towel and let rise at room temperature, 2 hours  
4. Meanwhile preheat the oven to 450°
5. Bake 10-13 minutes, or until golden brown. Cool completely before serving
6. Eat within 2-3 days of making, and store in an airtight container