How to Make It
Preheat the oven to 450°. Line 2 baking sheets with parchment paper. In a food processor, pulse the flours. With the machine on, pour in 1 cup plus 2 tablespoons of the water and process until a soft, evenly moistened dough forms. If necessary, add the remaining water, 1 tablespoon at a time. Divide the dough into 12 balls, cover with plastic wrap and let stand for 2 minutes.
On a lightly floured surface, roll out 4 balls of dough as thinly as possible and prick the dough all over with a fork. Transfer to a baking sheet. Repeat with 4 more balls of dough. Bake the matzo in the upper and middle thirds of the oven for about 12 minutes, until lightly browned and crisp; shift the sheets from top to bottom and front to back halfway through baking. Transfer the matzo to a rack. Repeat with the remaining 4 balls of dough.
Spelt and oat flours can be found at well-stocked specialty and natural-food stores.