For the Cake:
Preheat oven to 400 degrees F and grease a 9x13-inch baking pan.
Melt butter in water then add cocoa and shortening. Bring to boil, stirring well to incorporate the cocoa. Remove from heat.
Mix the sugar and flour together in large bowl, and add the cocoa mixture. Stir well. Add the buttermilk, soda and cinnamon, stir to combine. Add the vanilla and eggs, stir to combine.
Pour the batter into the greased baking pan and bake for about 20 minutes or until a toothpick inserted into the center of the cake comes out clean.
For the Frosting:
Begin making the frosting about five minutes before the cake is done. In a small saucepan, combine the butter, milk and cocoa, and bring to a boil. Whisk constantly until combined.
Remove from heat and stir in sugar, vanilla and 1/2 cup of the nuts. Stir briskly, mixing well, and spread on cake while both are still hot.
Sprinkle the remaining nuts, chopped Candied Ginger and pomegranate seeds on top.
Notes:
The frosting comes out very thick and hardens quickly so don't make ahead! If using pomegranate seeds as a topping, wait for the frosting to cool slightly on the cake before adding or the seeds will release their juice. Not an entirely bad thing to have little pools of pomegranate syrup on your cake....