2. With a wooden spoon, stir in the whole wheat flour and salt. Stir in the bread flour by the cupful until a shaggy dough is formed and pulls away from the sides of the bowl.
3. Place the dough on a lightly floured work surface and knead by hand, adding flour as needed to keep the dough from sticking. Knead until the dough is smooth and elastic, about 8 to 10 minutes.
4. Spray the inside of a clean bowl with a non-stick spray and place the dough in the bowl. Cover with plastic wrap and lay a kitchen towel over the top of the bowl to keep the warmth inside. Let the dough rise at room temperature until it has tripled in size. This will take about 1 1/2 to 2 hours. (Or let the dough rise slowly in the refrigerator overnight.)
5. Turn the dough out onto a lightly floured work surface and punch the dough down several times. Knead the dough for 5 minutes and return the dough to the bowl, cover with plastic and let rise until double in size, about 20 to 30 minutes (an hour or more if the dough has been refrigerated).
6. Turn the dough out onto the work surface and divide it into 4 equal pieces. Flatten each piece of dough into a rectangle, fold it into thirds and roll it into a cylinder about 16" long. Place the loaves in baguette pans or set them on the backside of a two cookie sheets sprinkled with cornmeal. Cover the loaves with a clean kitchen towel and let them rise at room temperature until doubled in size, about 45 minutes. If the dough has been in the refrigerator, rising time will be longer.
7. Meanwhile, place a baking stone on the middle rack of the oven and preheat it 450°F.
8. With a sharp knife, carefully make 3 or 4 diagonal cuts on each loaf, about 1/8" deep.
9. Place a bowl of boiling water on the bottom rack of the oven. The water will create steam in the oven and make a nice crust on the bread. Carefully transfer the loaves (in the bread pans, if you are using them) to the oven and place them on the baking stone.
10. Bake until the loaves are golden brown and they feel very light for their size, about 25 to 30 minutes. The best way to test for doneness is to hold a loaf with a kitchen towel in one hand and thump on the back of it with the other; if it sounds hollow, it's done. Let cool for at least 10 minutes before slicing.