Preheat the oven to 325°F. Lightly grease a 9 x 13-inch pan.
In a large mixing bowl, cream together the butter, oil, sugar, vanilla, baking soda, baking powder, and salt.
Add in the eggs. Stir in the sour cream alternately with the flour. Then add the cocoa powder and mix until incorporated and the batter is smooth. Fold in the zucchini and 2/3 cup chocolate chips. Batter will be thick.
Spread the batter to the edges of the prepared pan and bake the cake for 30 to 35 minutes, till the top springs back lightly when touched. Place pan on a wire rack to cool completely.
For the Chocolate Ganache
To prepare the frosting, heat the heavy cream in a saucepan over medium heat until simmering.
Remove the cream from the heat and pour it over the chocolate chips. Whisk to combine. It may take a few minutes of stirring for the ganache to come together, but I promise it will. The ganache will thicken as it cools.
Allow the ganache too cool until just slightly warm and still pourable. Pour the ganache over the cake and smooth with offset spatula. Allow frosting to set for about 30 minutes before serving.
Notes
*If you are using regular unsweetened cocoa powder, add an additional 1/2 teaspoon of baking soda.Store leftover chocolate zucchini cake in the fridge for up to 3 days.