1. Preheat oven to 350°.
2. To prepare cake, heat 3/4 cup milk in a small saucepan over medium-low heat 2 minutes or until warm; add chocolate chips, stirring until smooth. Cool.
3. Weigh or lightly spoon brown rice flour, potato starch, and tapioca flour into dry measuring cups; level with a knife. Combine flours and next 4 ingredients in a bowl; stir with a whisk.
4. Combine eggs and next 3 ingredients in a bowl; beat with a mixer at low speed until blended. Add chocolate mixture, beating until blended. Add flour mixture alternately with remaining 1 cup milk, beginning and ending with dry ingredients; beat until smooth. Pour batter evenly into 2 (9-inch) round cake pans coated with cooking spray and lined with parchment paper.
5. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove from pans. Cool completely on a wire rack.
6. To prepare frosting, combine powdered sugar and cocoa in a large bowl; stir with a whisk. Combine milk and vanilla. Place butter in a separate bowl; beat with a mixer at medium speed until creamy. Add powdered sugar mixture alternately with milk mixture, beating well after each addition until spreading consistency.
7. Place 1 cake layer on a plate; spread with 1 cup frosting. Top with remaining cake layer. Spread remaining frosting over top and sides of cake. Garnish with raspberries and mint sprigs, if desired.
Somebody get me a glass of milk! I almost forgot what chocolate cake tastes like—thanks for the reminder. Although a lot of gluten-free desserts turn out dry, this cake was very moist. The icing was definitely the "icing on the cake"! Very rich and the perfect complement to the cake. —Roxanne D. Osborne