Well, I still haven't found it, exactly. But I feel like I'm on the right track. I started using about (as of now, I'm not really measuring--so if I actually find a winner, I'll have trouble replicating it) a cup of kefir (that thin yogurt-like stuff I'm growing on my counter), a half cup of starter, a cup of coffee-ground sweet brown rice, 1/2 c sweet sorghum flour, and 1/2 c coffee-ground oat flour. I also added, for good measure, a little shake of xanthum gum (it helps hold together gluten-free recipes), one egg, about a teaspoon of baking powder, and, oops, today I forgot the salt. So it didn't really rise much, if at all. But at least when it baked today it rose incrementally. And it tastes great. So even though potato flour makes it rise more, I'm going to avoid it. There's nothing yummy about the smell of potato when making toast. Anyway, today's loaf at least made some pretense of rising. I will keep you posted.