My DD is gluten-free for medical reasons and she leans to recipes from the Gluten-Free Goddess on the internet.
I have tried 'Cup-4-Cup' which isn't too gritty but it is hideously expensive and the only place I can find it is at Williams Sonoma. The gluten-free Bisquick isn't bad and isn't pricey. Other than that I think you are tasting flour for grittiness and putting in all the Bob's Mill ingredients to come up with the cake mix or cookie mix. (we discovered that some flour - sorry don't remember which one - is an excellent exfolliant and after washing it off our hands we decided it might make a good substitute for oatmeal body scrub. Unless it clogs the drain. We also tried a brownie mix from the health food store and one batch seemed soggy, the other just an unappealing tough texture.
I know it can be done because we have bought scrumptious gluten free pastries from a specialty bakery ... unfortunately an hour away.
Good luck and let us know what you come up with that works!