Preheat the oven to 350°F (175°C). Grease three 9-inch round cake pans and line the bottoms with parchment paper.

Sift the cocoa powder into a bowl. Whisk in the hot coffee until smooth, then let cool for 10 minutes.

In a large bowl, whisk together the flour, sugar, baking soda, baking powder, and salt.

Add the vegetable oil, buttermilk, eggs, and vanilla to the cooled cocoa mixture. Whisk until fully combined.

Pour the wet mixture into the dry ingredients and mix until smooth. Divide evenly between the prepared pans.

Bake for about 30 minutes, or until a toothpick inserted in the center comes out clean.

Cool completely before removing from the pans.

To prepare the buttercream, sift together the confectioners' sugar, cocoa powder, espresso powder, and salt.

Beat the butter until light and fluffy, about 5 minutes. Gradually add the sugar mixture, then mix in the vanilla and heavy cream until smooth.

Heat the heavy cream until very hot and pour over the chopped dark chocolate. Let stand for a few minutes before whisking into a smooth ganache.

Assemble the Mocha Cake by spreading about one cup of buttercream over the first layer. Add a swirl of ganache and sprinkle with chopped espresso beans. Repeat with the second layer.

Frost the entire cake with the remaining buttercream and chill for 20 minutes.

Rewarm the ganache until pourable and drip it over the chilled cake. Decorate with buttercream swirls and whole chocolate-covered espresso beans if desired.