JAN SCHAT'S FLATBREAD

Steps:

• Make biga:
• Whisk yeast into 120 grams (‚ cup) warm water to dissolve and stir in flour. (Mixture will be dry.) Knead in remaining 55 grams (a scant 1/4 cup) water and knead in bowl until a dough is formed. Turn out onto a clean surface and knead until smooth, about 5 minutes. (Do not add extra flour; biga will become less sticky as it is kneaded.) Put in a clean bowl and cover tightly with plastic wrap. Chill in refrigerator 16 to 18 hours. (Biga will not rise perceptibly.)
• Let biga stand, still covered, in a warm place until instant-read thermometer registers 75-78°F, about 1 hour.
• Make flatbread dough:
• Chop 170 grams (or scant half) of biga recipe. (Leftover biga keeps, covered and chilled, 2 days.) Whisk yeast into 60 grams (1/4 cup) warm water to dissolve in a large bowl and stir in yogurt, chopped biga, whole-wheat flour, salt, oil, and bread flour. Knead in enough of remaining 60 grams (1/4 cup) warm water, a little at a time, to make dough workable. (Dough will be sticky.)
• Turn dough out onto a very lightly floured surface and knead, occasionally scraping up dough stuck to surface with dough scraper, 10 minutes. (If dough becomes too sticky to knead easily, periodically flour hands, not work surface; dough will become less sticky as kneaded.)
• Gradually knead in any remaining water and continue to knead dough until smooth, satiny, and stretchy, about 10 minutes. Put in a clean bowl and dust very lightly with flour. Cover with plastic wrap and let rise in a warm place 1 hour.
• Turn dough out onto a very lightly floured surface and stretch into a rectangle. Fold into thirds, like a letter, then stretch and fold again in same manner. Return to bowl and let rise, covered, 1 hour. Repeat stretching and folding process and let rise again, covered, 1 hour.
• Halve dough and shape each half into an 8-inch log on work surface. Dust very lightly with flour and let rise, covered loosely with plastic wrap, 30 minutes.
• Bake flatbread:
• Put pizza stone on rack in middle of oven and preheat to 525°F. (Allow 1 hour to preheat with stone.)
• Stretch each dough log into a roughly 13- by 6-inch rectangle and brush lightly with water. Dimple dough with your fingertips and sprinkle with nigella seeds and sea salt. Dimple dough again and let stand, loosely covered with plastic wrap, at room temperature 45 minutes.
• Generously sprinkle baker's peel with cornmeal. Holding 1 rectangle at each end, pick up and transfer to baker's. (Dough will stretch.) Re-form into rectangle and dimple once more. Jerk peel once or twice; if dough sticks, lift and sprinkle more cornmeal underneath.
• Working quickly, mist oven with 4 squirts of water from spray bottle. Line up far edge of peel with far edge of stone and tilt peel, jerking it gently to start dough moving. When edge of dough touches stone, quickly pull back peel to transfer dough to stone. Mist oven again with 4 squirts from spray bottle and bake flatbread until golden brown, 6 to 10 minutes. Transfer to a rack and while still hot, brush with some of butter.
• Sweep burned cornmeal off pizza stone with a cloth before baking remaining flatbread in same manner.
• Serve warm or at room temperature.