Preheat oven to 350 degrees F. Line the inside of 9×5 inch baking pan non-stick foil.Stir together the rice flour, tapioca flour and salt; set aside.In a saucepan, melt butter over medium heat. When butter starts to melt and coats pan bottom, add unsweetened chocolate and reduce heat to low. Stir constantly until chocolate is melted.
Add 1/2 cup of the sugar to melted chocolate and stir over low heat for about 40 seconds.
Remove chocolate mixture from heat and let cool for about 5 minutes. Stir in vanilla.Meanwhile, using an electric mixer (hand-held or stand okay), beat eggs for a full 2 minute or until foamy and light. Gradually add remaining 1/2 cup of sugar to eggs and continue beating for another minute.Using a rubber spatula, fold a small amount (about 1/3 cup) of the egg mixture into the warm chocolate mixture, then fold the lightened chocolate into the bowl with the egg mixture. Stir in the rice/tapioca flour/salt mixture, being careful not to over-mix.
Pour into pan and bake for 25-28 minutes or until top is set.
Let cool completely.
Transfer to refrigerator and chill for a few hours or overnight. Lift from pan and cut.
