Step 1

Preheat oven to 350 degrees F. Coat 2 (9-inch) round cake pans with cooking spray and lightly dust with flour. In a medium bowl, mix flour, cocoa powder, baking soda, baking powder, and salt; set aside.

Step 2

In a large bowl, using an electric mixer, beat butter and sugar until creamy. Beat in eggs, sour cream, and vanilla until combined. Slowly add dry mixture and water to creamy mixture and beat just until blended.

Step 3

Pour batter into prepared pans and bake 28 to 34 minutes, or until toothpick inserted in center comes out clean. Let cool 15 minutes, then remove to a wire rack to cool completely.

Step 4

To make frosting, in a large bowl, using an electric mixer, beat butter until creamy. Add remaining ingredients and blend until smooth.

Step 5

Place one cake layer upside down on a serving platter and frost top. Place second layer over first and frost top and sides. Serve or refrigerate until ready to serve.