Preheat the oven to 350F (180C) degrees and position a wire rack on the bottom ⅓ of the oven.
Brush a 12-cup capacity bundt pan with pan release* or grease and dust with cocoa powder. Be sure to get inside all the creases of the pan.
In a large bowl whisk together the flour, cocoa, baking soda, salt, and sugar.
In a separate large bowl beat (or whisk) together the oil, eggs, vanilla extract, sour cream, and buttermilk.
Beat the flour mixture into the wet ingredients (I usually do this about ½ at a time).
Carefully whisk the boiling water into the batter.
Pour the batter into the prepared pan, and bake for 50-60 minutes - or until a toothpick comes out clean.
Cool in the pan for 20 minutes, then carefully invert the pan onto a wire rack to slide the bundt cake out. *Do not try to invert the pan immediately, or wait until the cake is fully cooled to invert.
Chop the chocolate into very small pieces and place in a heatproof bowl.
Heat the cream in a small saucepan, stirring constantly to prevent burning.
Once the cream is very hot (but not quite boiling), pour the cream over the chopped chocolate.
Let sit for 2 minutes, then whisk until smooth. Whisk in the corn syrup.
Transfer the cake to a serving plate.
Drizzle or pour the chocolate ganache over the cooled cake.
1.Dutch-process cocoa powder preferred. 2. Eggs, sour cream and buttermilk should be at room temperature. 3. 50-70% dark chocolate or semi-sweet chocolate works best. Do not use bittersweet chocolate.4. To make your own pan release, beat together ¼ cup shortening, ¼ cup vegetable (or canola) oil, and ¼ cup flour. Use a pastry brush to brush the inside of the bundt pan. Store leftover pan release in an airtight container in your pantry. Store leftovers in an airtight container at room temperature for up to 4 days, or in the fridge for up to 7 days. Note that the ganache can discolor if placed in the fridge. Un-glazed cake can be frozen.To freeze - cool the cake fully as instructed in the recipe. Then wrap the cake in the plastic wrap going around the ring shape (ie - do not wrap over the hole in the middle). Then place the cake in the a freezer safe container and freeze for up to 2 months. Thaw in the fridge.