1. In electric mixer, combine 1/4 cup water and yeast. Let stand until yeast is creamy, 10 minutes. Add remaining water, both flours, and salt; mix on low speed using paddle, 2 minutes. Change to the dough hook and mix on medium-low speed until dough is firm, 8 minutes. Or knead by hand, 15 to 20 minutes.

2. On a floured surface, knead dough by hand into a ball. Place smooth side up in an oiled bowl and cover; let rise in a warm place until doubled in bulk, about 2 hours.

3. Punch down dough; fold over on itself 4 or 5 times. Turn the folded side down. Cover; let rise in warm place until doubled in bulk, about 1 hour.

4. Line 2 baking sheets with parchment; flour them. Turn dough onto floured surface and cut in half. Pat one piece into an 8-by-11-inch rectangle. Fold in half widthwise and press down to seal edges. Repeat, folding 2 more times; place dough, seam side down, on unfloured surface. Roll it back and forth, gently stretching it out to 28 inches long. Pinch ends together, forming a circle. Transfer to prepared baking sheet; correct shape; cover loosely with oiled plastic wrap. Repeat the whole process with other piece of dough. Let rise in warm place until doubled in bulk, about 45 minutes. Thirty minutes before final rise is completed, place a baking stone, if using, in oven and a baking pan on lowest shelf. Heat oven to 450 degrees.

5. Dust loaves with flour. Hold scissors (with blades flat) at a 45 degree angle to dough; make a cut across the width three-quarters of the way through. Fold the V-shaped flap of dough to right. Keep making cuts every 1 1/2 inches and folding alternately to left and right. Repeat with other loaf.

6. Place baking sheets directly on the baking stone, if using. Pour 2 cups very hot water into heated baking pan to create steam; bake until medium golden brown and hollow sounding when tapped on bottom, 20 to 25 minutes. Cool on wire rack for at least 30 minutes before slicing.