Step 1Dissolve the yeast in 1/4 cup of the water in a large bowl. When it starts to foam, stir in the remaining water. Combine 3 cups of the all-purpose flour with the whole-wheat flour and salt. Add to the yeast mixture, stirring until blended. Beat in additional flour as necessary to form a ball.
Step 2Knead the dough on a floured board until smooth and elastic, 10 minutes. Transfer to a greased bowl and cover ith plastic wrap and a towel; let rise in a warm place until double in volume, 1 1/2 to 2 hours.
Step 3Punch down and form into a ball. Roll it in flour; set on a baking sheet sprinkled with 2 tablespoons of cornmeal. Cover with an inverted pot 9 inches or more in diameter. Leave in a warm place 1 hour.
Step 4Remove middle rack from oven; place a pizza stone on bottom rack. Sprinkle remaining cornmeal on the stone. Heat oven to 450 degrees.
Step 5Remove the pot from the bread and make several slashes on the top of the bread with a sharp knife. Slide the bread onto the hot stone. Replace the pot. Bake 15 minutes. Reduce the heat to 400 degrees and bake 15 minutes longer. Remove the pot. Continue baking until browned and the crust just begins to smell like toast, 25 to 30 minutes longer.