1. Dissolve sugar and yeast in 1 cup plus 2 tablespoons warm water in a large bowl; let stand 5 minutes. Weigh or lightly spoon flours into dry measuring cups; level with a knife. Add bread flour, 3 ounces (about 3/4 cup) whole-wheat flour, yogurt, oil, and salt to the yeast mixture; beat with a mixer at medium speed until smooth. Turn the dough out onto a floured surface. Knead dough until smooth and elastic (about 10 minutes); add enough of remaining whole-wheat flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel sticky). Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, for 45 minutes or until doubled in size.
2. Position the oven rack on the lowest shelf.
3. Preheat the oven to 500°.
4. Divide dough into 8 portions. Working with one portion at a time, gently roll each portion into a 5 1/2-inch circle. Place 4 dough circles on each of 2 baking sheets heavily coated with cooking spray. Bake, 1 sheet at a time, at 500° for 8 minutes or until puffed and browned. Cool on a wire rack.