Preheat the oven to 350°F. Grease three 9-inch round cake pans and line the bottoms with parchment paper. Lightly grease the parchment to make releasing the cakes easier.

Whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt. In another bowl, whisk the oil, eggs, sour cream, buttermilk, and vanilla. Add the dry ingredients to the wet mixture, then slowly stir in the hot coffee or water until the batter is smooth.

Divide the batter evenly between the prepared pans. Bake for 22–25 minutes, or until a toothpick inserted into the center comes out clean. Cool in the pans for 10 minutes, then transfer to a wire rack and cool completely.

Drain the cherries, reserving ¾ cup of the syrup. Simmer the syrup with the cherry liqueur, if using, over low heat for about 8–10 minutes, until reduced to roughly ¼ cup. Let it cool, then cut most of the cherries in half while keeping a few whole for decoration.

Beat the cold heavy cream, powdered sugar, and vanilla with an electric mixer until medium peaks form. Keep the whipped cream chilled until ready to assemble the cake.

Place the chopped chocolate in a heatproof bowl. Warm the heavy cream until it just begins to simmer, then pour it over the chocolate. Let it sit for 2 minutes before stirring slowly until smooth and glossy. Set aside to cool slightly.

Level the cake layers if necessary. Place one layer on a serving plate, brush with cherry syrup, and spread with whipped cream. Add half of the sliced cherries, then repeat with the second cake layer, syrup, whipped cream, and remaining cherries. Place the final layer on top, cover the cake with the remaining whipped cream, and smooth the sides. Spoon the ganache over the top so it gently drips down the sides. Decorate with chocolate shavings and whole cherries, then refrigerate for at least 30 minutes before slicing.