(You can change the types and ratios of flours- just keep in mind that the Brown Rice flour is not as fine as others, so in cake you probably don't want to use a lot of it- but you could. If you did you may need to add more milk, or another egg.)
Pre-heat your oven to 350
2/3 cup White Rice flour (the sticky kind- you can get it at the Asian markets)
1/3 cup Brown Rice flour
1/3 cup Sorghum flour (Bob's Red Mill)
1/2 tea. Salt
1 & 1/4 tea. Baking Powder
1/2 tea. Xanthan Gum (you could use unflavored gelatin- look up how much to substitute)
1/4 cup Butter
1/2 cup Sugar
3/4 tea. Vanilla
2/3 cup Milk
Cream the butter (on medium speed), about 30 seconds.
Add sugar & vanilla; beat till well combined.
Add egg(s) beating 1 minute after each. Add flour mixture and milk alternately to beaten mixture, beating on low speed after each addition just till combined.
Turn into greased pan (8x8 or equivalent) Bakes anywhere from 20 to 30 minutes. Toothpick will come out clean.
Cool 10 minutes in pan.