Preheat oven to 350°F. For the Cupcakes, mix cocoa powder, cornstarch, sorghum flour, tapioca flour, xanthan gum, baking powder, baking soda and salt in medium bowl. Set aside.
Beat granulated sugar and oil in large bowl with electric mixer on medium speed until well blended. Add melted chocolate; mix well. Beat in eggs, 1 at a time. Stir food color and vanilla into buttermilk. Gradually beat in flour mixture alternately with buttermilk mixture on low speed until just blended. Do not overbeat. Spoon batter into 24 paper-lined muffin cups, filling each cup 2/3 full.
Bake 23 to 25 minutes or until toothpick inserted into cupcake comes out clean. Cool in pans on wire rack 5 minutes. Remove from pans; cool completely.
For the Frosting, beat cream cheese, butter, sour cream and vanilla in large bowl until light and fluffy. Gradually beat in confectioners’ sugar until smooth. Frost cooled cupcakes with Frosting.