Coat two 8-inch baking pans with nonstick cooking spray. Heat oven to 350 degrees F.
In a large bowl, whisk together sour cream and oil (it will look curdled). Sift flour and cocoa powder into the bowl. Add sugar. Beat until just moistened. Add eggs and beat over medium-high power for 2 minutes, until smooth and fluid. Stir in food coloring and vanilla. Divide equally between prepared pans.
Bake layers at 350 degrees F for 25 to 28 minutes or until toothpick inserted in center of layer comes out clean. Cool in pans on wire rack for 10 minutes; then invert cakes and remove pans. Cool completely.
Once layers are cool, place one on a cake stand or platter. Top with 3/4 cup prepared frosting, spreading level. Top with second cake layer, and frost side and top of cake with remaining frosting. Chill slightly before serving. Makes 12 servings.