In a bowl of a stand mixer, whisk 350g warm water with 225g sourdough starter until it looks like milk.
Add 600g flour (300g all-purpose flour and 300 whole-grain kamut).
Add 15g salt and 1 teaspoon dry yeast, if using.
Using a stiff spatula or a spoon, mix everything until it looks like torn up pieces.
Connect the bowl to the mixer fitted with a dough hook. Knead for 5-10 minutes.
Sprinkle the dough with flour, knead with your hands into a smooth ball.
Place the dough in a greased large bowl, cover, and leave to ferment at room temperature. This might take anywhere from 5 to 10 hours: look at the dough, not the time. It should rise significanly and look soft and puffy.
Once ready, divide the dough into 2 pieces, shape them into long boules, about 9-10" long.
Place boules on parchment covered cookie sheet. Cover with plastic or a tea towel. Leave to rise for 1-2 hours. You should see a significant increase in size.
Once ready to bake, preheat oven to 425ºF.
Slash the dough with a bread knife or lame. I usually do 3 diagonal cuts but one long one in the middle looks pretty too.
Place the boules in the over, and sprinkle oven generously with water. Bake for 10 mintues.
Reduce temperature to 350ºF, and bake for 15 more minutes.