Add a cup of start to a large metal bowl. Add 1 cup of cool water and whisk well. Add remaining 2 cups water, flour, salt, and yeast. Mix well. The dough will be sticky, not kneadable. Cover the bowl with a tea towel and leave for 12-15 hours.
After the 12-15 hours your dough should look bubbly. Flour your counter and dump the dough onto the counter. Knead the dough a few times. It is really sticky so its less like kneading and more like turning the dough over a few times in the flour.
Place dough into greased bowl, and cover again with your towel. Let rest until you are ready to cook, but at least 45 minutes.
Preheat the oven to 450 degrees with your Dutch oven inside. Sprinkle cornmeal in the bottom of the dutch oven and dump your dough into the dutch oven. Cover and bake for 30 minutes. Remove lid and cook for another 15 minutes.
Notes
Be sure to add equal parts water and flour to your start to grow more. Keep your start refrigerated.