Sourdough Bread
Once you have your levain ready, gather the following ingredients.
500 grams of levain, stirred together until everything is blended evenly
100 grams sorghum flour
100 grams brown rice flour
200 grams potato starch
125 grams cornstarch
300 grams/milliliters warm, filtered water
1 1/4 tsp psyllium powder
1 1/2 tsp salt
Mix the flours and psyllium together with a whisk, breaking up any starch lumps, then mix them with the levain and water. I used a spoon one time, and the KA the next. The KA does a nice job and makes things a little easier, but it's not necessary. Once everything is mixed, let it sit about 15 minutes to hydrate. Now mix in the salt.
Because the starter contains 200 grams of flour and 300 grams of water, at this point, you have a very soft dough at about 83% saturation (725 g flour, 600 ml water). The texture is like quicksand, and it will seem way too wet for bread dough. Pour it into your cast iron container or dutch oven that you have lined with parchment. (I know this is a terrible photo, but it's the best I have of the texture.)
Set the pot aside, covered with plastic or the lid, and let the dough rise. I don't have a photo of the risen dough because it went really fast the last half hour and I feared disastrous results. To prevent my mistake, don't let the dough rise more than about 1 1/2 times the original bulk, especially if you have a really good starter going. You'll be using a cold oven, and the final rising will happen then. You can make a mark on the parchment when you pour in the dough to know when it has risen properly.
Once the dough is risen, place the pot, cover on (phenolic knob off

), into your oven, and set the temp to 450 degrees. Bake for an hour from the time you start the oven, not from the time it reaches temperature, then take off the lid and let the crust brown some more. Here's mine from tonight. It could stand to be browner, but we were hungry.
As you can see, the dough fell a little because I overproofed it, but it recovered and domed up because of the cold oven, and especially because levain is much more forgiving than yeast. So here's the money shot.
This is fantastic bread. Not great gluten-free bread, great bread in its own right with sourdough tang and a nice crust from baking in the cast iron pot like no-knead bread. I could serve this to guests and I would be really surprised if anyone could tell that it is gluten free. Plus, its more than half whole grain, which means we're eating more healthful bread than when we ate wheat bread.
Just like the yeast bread, this formula above is a ratio, and you can change it around at will. Just remember that the levain is 40% flour and 60% water, and keep your final ratio at about 83% hydration with a little less than a teaspoon of psyllium per 500 grams of flour. I'll experiment with some other starches, but the bread seems to need these light ones for lift.
Edited to add - the hardest part about GF bread is that you really do have to wait for it to cool before you cut it. This loaf cooled about a half hour and cut OK.
Happy bread making!