Soak prunes in warm water for a couple hours if they're very dry, or for 30 minutes to 1 hour if they're not, essentially until they're rehydrated, soft and plump. Drain the water. Chop into small pieces. Set aside.

Preheat oven to 375F. With the baking rack in the middle.

To assemble the cake you need a 9 inch round, 5 inch tall spring form. If you don't have one, just bake wider cake layers (10"-11") and then you can assemble it without a ring.

Draw a 9 inch circle on 2 pieces of parchment paper. Flip upside down. Pour 1/3 cup cake batter and spread around evenly (place the parchment paper on a silpat sheet or something nonskid, to help the parchment paper stay in place as you spread the batter) within the drawn circle.

Draw a 10" or 10.5" circle on 2 pieces of parchment paper. Flip upside down. Pour 1/2 cup cake batter and spread around evenly (place the parchment paper on a silpat sheet or something nonskid, to help the parchment paper stay in place as you spread the batter) within the drawn circle.

Bake for 6 minutes or until cooked through. Remove from oven, peel off parchment paper, and transfer the cake to a cooling rack. Reuse the parchment paper for the next cake layer.

Working with 2 pieces of parchment allows you to spread the batter one one piece of parchment paper as the other one is baking.

Combine all ingredients in a bowl of a mixer and whip on high until increased in volume and raising the whisk out of the frosting leaves a visible ribbon that does not disappear, about 5 minutes.

You need to assemble the cake in a 5 inch tall adjustable cake ring or a cake spring form for best results as the frosting is not very stiff and will probably run off the layers as you stack them. If your spring form or adjustable cake ring is not tall enough, you can line the inside of the cake ring with parchment/wax paper/acetate strip 5-6 inches tall, overlapping the ends by about 4 inches to keep the frosting from escaping. Theoretically it's probably possible to layer the cake without it, but it probably would get a little messy, beware.

Place the cake ring in the middle of the board or a cake platter.

Put a dab of frosting in the middle of the platter and cover with one cake layer. Fasten a ribbon around the cake ring to fit snuggly around the cake layer. Top with about 1 cup Sour Cream frosting for the 9 inch layers, or a little more for the 10" inch layers, and spread it around. Sprinkle about 6-8 chopped prunes over the top.

Repeat with the remaining cake, frosting and prunes until no more cake remains, putting the last cake layer bottom side up and covering it in only a thin layer of frosting and no prunes.

Refrigerate the cake and the remainder of the frosting for 2 hours before removing the cake ring off the cake.

Unmold the cake from the cake ring and cover it in the remaining frosting, concentrating mainly on the sides of the cake and not the top.

Prepare 1/4 cup ganache, bring it to room temperature, fill a ziplock bag with it then with the same motion as you would write letter M with (going up and down about 1/2 inch) make a drizzle around the edges of the cake. Sprinkle 1/2 cup of chopped walnuts over the top of the cake.

Place a couple green twigs from a christmas tree branch over the cake if decorating for a Christmas or New Years.