Preheat oven to 350 degrees F (175 C). Spray a 12-15 cup non-stick bundt cake pan with non-stick cooking spray. Dust lightly with flour and cocoa powder (about 0.5 Tbsp of each). Shake out excess.

In a medium mixing bowl, whisk together flour, granulated sugar, baking soda, and salt. Set aside.

In a large mixing bowl, whisk together melted butter, hot water, and cocoa powder.

Add the flour mixture to the butter mixture and using an electric hand mixer, blend until well combined.

Add sour cream, eggs, and vanilla extract. Mix until well combined.

Pour the mixture into the prepared bundt pan.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, about 40-50 minutes.

Let cool in the pan for 8-10 minutes, then run a knife down the sides of the cake to ensure it's loose. Invert onto a wire rack to cool completely, at least 30 minutes.

To make the chocolate ganache, place the chopped bittersweet chocolate in a medium heat-proof mixing bowl.

Heat heavy cream in a small saucepan on the stove until just simmering. Pour the hot cream over the chocolate, making sure to submerge the chocolate if needed.

Let the mixture rest for 4 minutes, then stir until melted and smooth. Pour the chocolate ganache over the cooled cake. Let cool slightly before serving.

Cut into slices and serve.