Prepare a 9×13 pan with either butter or non-stick spray.
In a small bowl, beat egg whites until soft peaks form. Set aside.
In a large bowl, combine the brown rice flour, corn starch, 2 cups sugar, and guar or xanthan gum. Mix in salt, baking powder, and 3 teaspoons vanilla. Add egg yolks and mix well. Mixture will be more like a dough. Don’t worry. Fold in egg whites and combine well.
Pour mixture into pan. Bake for 30-40 minutes.
While cake is baking, mix 1/3 cup cream, evaporated milk, and condensed milk together with whisk. Set aside.
In a separate bowl, mix 1 2/3 cup cream, 2 teaspoons vanilla and 1/8 cup sugar for frosting. This will take about 5 minutes. Set aside.
Allow cake to sit for 10 minutes once baking is complete.
With a fork, prick about 12-15 holes in the cake. Also lift the sides to allow the mixture to be spread all over. Pour the pour over mixture on top of the cake.
Set cake in the refrigerator to cool.
After 10-15 minutes in the refrigerator, spread frosting on top and place back into refrigerator until serving.
Tapioca or corn starch may be used.
Guar or xanthan gum may be used.