Arrange oven rack in the middle of the oven. Heat oven to 350 degrees.
Use a little butter and toweling to grease two 9-inch round cake pans. Line bottoms with parchment paper and place in the pan. Butter the paper and then flour the paper.
In a large bowl, whisk flour, pumpkin pi spice, baking soda, baking powder and salt together. Set aside.
Using an stand or electric mixer, cream 8 tablespoons butter and granulated sugar together until fluffy. Beat in eggs one at a time. Next, stir in pumpkin purée. Stir in flour mixture about half a cup at a time until smooth. Gently fold in chocolate chips.
Divide batter into the cake pans and bake for about 35 minutes, or until a tester inserted in center comes out clean. Cool cakes in pans for 10 minutes, run a knife around edges, place upside down onto racks or counter, and peel off paper. Let cakes cool completely.
While cakes cool, mix 12 tablespoons butter and confectioners' sugar together with a stand r electric mixer. Mix in chocolate and vanilla extract and beat until smooth. Add milk by the tablespoon, blending well after each addition, until it reaches spreading consistency. If you need to use more milk please add slowly.
Place one cake layer, smooth side up, on a platter. Ice top with a crumb coat. Place second layer, smooth side down, on top; ice top and sides of cake with a crumb coat. Complete icing the cake with the remainder of the frosting.