To make the sponge, proof the yeast in 1/8 cup of the warm water until the mixture is creamy. Add this to the rest of the warm water in a large bowl and add the flour a handful at a time mixing it in with a wooden spoon. When the ingredients have been thoroughly combined, the sponge will be very soupy. It can be left in the same bowl if it is large enough for the sponge to triple.
Let the sponge rise, covered, in a warm spot for 8 to 10 hours.
To make the dough, place the sponge and the salt in a food processor fitted with the plastic blade. Pulse to combine. Add the 0.25 cup of cold water and process for about 30 seconds. Add the remaining flour, 0.25 cup at a time, pulsing 3 or 4 times after each addition. The dough will come away from the side of the bowl but it will be quite sticky. Scrape down the sides of the bowl and pulse again 2 or 3 times.
Dust the dough with a handful of extra flour and then scrape the dough out of the processor onto a floured work surface. The extra flour will make it possible to handle the wet dough. Knead the dough for a minute or so to work out any lumps and shape it into a tight, round ball. Do not be afraid to use up to 0.5 cup of extra flour to keep the dough from sticking.
Cover with plastic wrap or a damp towel and let rise in a warm place for 2 to 3 hours. When the dough has doubled, turn it out onto the work surface. This would normally be divided to make 2 baguettes.
Preheat oven to 450F. Place baguettes in oven and immediately reduce heat to 425F. Bake for 20 to 25 minutes or until golden brown.
You might want to look at the book _The Village Baker_ by Joe Ortiz.