Preheat oven to 350°F.
Grease and flour two 9-inch round cake pans.
Beat butter and sugar in large bowl with electric mixer at medium speed until light and fluffy.
Beat in egg and vanilla until blended.
Combine flour, cocoa, baking soda and salt in medium bowl.
Add flour mixture to butter mixture, alternately with buttermilk and sour cream, beginning and ending with flour mixture.
Beat well after each addition.
Divide evenly between prepared pans.
Bake 30 to 35 minutes or until wooden toothpick inserted in centers comes out clean.
Cool in pans 10 minutes.
Remove from pans to wire racks; cool completely.
Meanwhile, prepare Light Ganache Filling.
Place one cake layer on serving plate.
Spread with Light Ganache Filling.
Top with second cake layer.
Prepare Dark Chocolate Glaze.
Pour over top of cake.
Immediately spread glaze over side and top with spatula until smooth.
Refrigerate cake at least 30 minutes to set glaze.
Garnish as desired.
Store tightly covered at room temperature.