Chocolate Blackout Cake

For the cake:
Unsalted butter for the pans
3 c cake flour
1 3/4 t baking soda
1 lb unsalted butter, softened
2 lb light brown sugar
7 large eggs
2 t vanilla extract
2 1/2 c cold water
1 c sour cream
1 lb unsweetened chocolate, melted and cooled

For the icing:
1 lb unsweetened chocolate, finely chopped
2 c heavy cream
2 1/2 c sugar
1 1/2 T light corn syrup
1 T vanilla
2 c sour cream
3/4 c chocolate chips

Preheat oven to 325*. Butter the bottoms of four 9 in round cake pans and line with parchment paper.
Sift together the flour and baking soda. In a medium bowl, cream the butter and sugar. Add the eggs and vanilla and mix thoroughly. Add the dry ingredients in three parts, alternating with the cold water. Mix completely. Add the sour cream and melted chocolate and mis until incorporated.
Divide the batter evenly among the prepared pans. Bake for 30-40 minutes, until the cakes have puffed and pulled away from the sides of the pans. Cool the cakes in their pans on a rack for 15 minutes. The cakes will sink to half their height. Remove them from their pans and cool completely on racks.
To make the icing, place the chopped chocolate in a large mixing bowl. Heat the cream, sugar and corn syrup in a medium saucepan just to boiling. Pour over the chopped chocolate, then slowly stir until smooth. Add the vanilla and allow to cool completely; then beat in the sour cream. The icing should be glossy.
To assemble your cake, place one cake layer on a plate. Top it with 1/2 c of the icing and 1/4 c chocolate chips. Repeat with next two layers. Top the cake with the final layer and cover the entire cake with remaining icing. Store covered at room temperature.