For cakes, preheat oven to 350 °F. Grease and flour (with brown rice flour)
2 8-inch cake pans.
Melt chocolate and butter in a bowl over a pot of barely simmering water and stir until melted. Set aside to cool.
Separate whites and whip with salt until foamy. Gradually add sugar and whip until whites hold a stiff peak when beaters are lifted. Add yolks and vanilla and whip until incorporated, about 30 seconds. Add cooled chocolate and beat in on low speed or fold in by hand. Scrape batter into prepared pans and spread to level. Bake for 25 to 35 minutes, until a tester inserted in the center of the cakes comes out clean. Cool cakes completely in pans before turning out (center of cakes will fall as they cool).
For filling, melt chocolate and butter over a pot of barely simmering water, stirring until melted. Cool for 10 minutes, then stir in sour cream, vanilla and honey. Add icing sugar and stir in, adding hot water as needed to achieve spread able consistency.
To assemble, gently tap out first cake layer upside down onto serving plate. Spread filling over top of cake, and top with second cake layer. Dust with icing sugar and chill before serving. Pull cake from fridge 30 minutes before slicing.