Whisk the apple cider vinegar into the nondairy milk.
In the bowl of a stand mixer with the dough hook attached, or in a large bowl if kneading by hand, place the sourdough starter. Add the sugar, warm water and almond milk mixed with vinegar and mix together on low speed or by hand.
Add the flours and xanthan gum directly into the bowl, one by one, kneading a little as you go along so they are thoroughly incorporated. Knead for a couple of minutes until everything is well incorporated and you have a tacky, slightly sticky dough. If your dough looks dry, drizzle in a little more water and knead.
Drizzle in the oil and knead for a couple more minutes until the oil is absorbed.
Remove the dough to a countertop and knead slightly before shaping into a boule. You might want to oil your hands lightly before handling the dough. It should be slightly tacky but still quite supple.
Place a parchment paper inside a bowl (I just use my stand mixer bowl for this) and sprinkle it liberally with any of the gluten-free flours (I used the rice flour)
Place the boule on the parchment, cover loosely with a kitchen towel (or a shower cap), and place overnight or about 10 hours in a warm place, like the oven with the pilot light on.
About a half hour before baking, preheat the oven to 500 degrees Fahrenheit with a 3 or 4 quart dutch oven inside it. Carefully, taking all the precautions you need and with oven mitts on, remove the dutch oven to the countertop. It will be screaming hot so be very, very careful handling it and do not touch the surface at any time without your mitts on.
Carefully, pick your boule up by the parchment paper and roll it quickly into the dutch oven, so the seam side at the bottom is now on top. Cover with the dutch oven lid and place it back in the oven.
After 30 minutes, remove the lid and turn the heat down to 450 degrees. Bake another 20 minutes.
Remove the dutch oven to a rack and let it stand until it is completely cool. The bread should unmold quite easily but if it doesn't, run a knife along the sides of the pot to help it along.