3 oz dark chocolate (70% cocoa or greater), roughly chopped
1 tsp organic unsalted butter
1 tbsp 1% milk
Prepare custard: In a small saucepan, heat 1 cup milk on medium until small bubbles form around edge, 3 to 4 minutes. In a heat-proof bowl, whisk one egg, rice flour, 1 1/2 tbsp cane juice and 1 tsp vanilla until thick. Slowly whisk in warm milk until smooth. Return to pot and bring to a boil on medium, stirring constantly. Cook, stirring, until pudding-like, about 30 seconds. Press mixture through a fine mesh sieve set over top of a small bowl. Cover custard surface directly with plastic wrap. Refrigerate for 1 hour.
Preheat oven to 350˚F. Mist two 8-inch round cake pans with cooking spray and line bottoms with 8-inch rounds of parchment paper. In a medium bowl, sift spelt flour, baking powder and salt. In a large bowl, use an electric hand mixer to beat three egg whites until foamy. Add 1 tbsp cane juice and beat until stiff peaks form. In a small bowl, combine 1/4 cup milk, melted butter and 1/2 tsp vanilla.
In a separate large bowl, use an electric hand mixer to beat remaining two eggs and 4 tbsp cane juice until thick. With a rubber spatula , gradually fold in egg white mixture until no white streaks remain. Gradually fold in flour mixture until just incorporated. Fold in milk mixture.
Divide batter among cake pans. Bake for 15 to 18 minutes, until golden brown and a toothpick comes out clean when inserted in center. Let cool in pan for 5 minutes. Invert onto a wire rack. Remove parchment from bottoms and cool completely. Cover top of one cake with custard; top with remaining cake.
Prepare glaze: In a heat-proof bowl, set over top of a pot of gently simmering water; melt chocolate and 1 tsp butter, stirring constantly. Remove from heat and stir in milk. Immediately spread over top of cake.