Grease and lightly flour a 12 cup bundt cake pan.

Preheat the oven to 350 degrees Fahrenheit. In the bowl of an electric mixer, mix together chocolate cake mix, chocolate instant pudding and pie filling, milk, sour cream, eggs, and vanilla. Scrape down the sides with a spatula throughout the process. Stir in 2 c. semi-sweet chocolate chips and chopped walnuts (nuts are optional).

Spread batter evenly around prepared bundt cake pan. Bake for approximately 37-38 minutes, or just until a toothpick inserted into the center comes out clean. Cool in the pan on a wire rack for 20 minutes. Then run a butterknife carefully around the edges of the pan to help release it. Carefully invert the cake onto the wire rack and allow it to cool completely.

To make the ganache, melt unsweetened chocolate and butter in a medium sauce pan over the stove top on low heat, stirring constantly. Remove from heat. Stir in powdered sugar, alternately, with milk (a Tablespoon at a time), until a nice consistency is reached. Stir in vanilla extract. Pour ganache over cake. Sprinkle with mini chocolate chips, if desired.