I found this recipe in an old (non-raw) book in my house called Healing With Whole Foods. It's a raw recipe, but it doesn't call for sprouted oats. I didn't soak/sprout the oats at all and it came out nicely, but please let me know how it comes out if you choose to sprout first.
1 cup raw oat groats (sprouting is optional)
1 cup water or rejuvelac
1/2 teaspoon raw miso (only if not using rejuvelac)
Blend all ingredients in Vitamix or food processor. I found it easiest to grind the oats to a powder first, and then add the liquid but I'm sure it would work either way. Transfer to a lidded container and leave in a warm place for 6-11 hours until it reaches the desired sourness. Yum!