Preheat the oven to 350°F (175°C). Grease two 8-inch cake pans and line the bottoms with parchment paper.
Mix dry ingredients: In a large bowl, sift flour, cocoa powder, baking powder, baking soda, and salt.
Mix wet ingredients: In a separate bowl, whisk together eggs, sugar, oil, vanilla, and buttermilk.
Combine and finish batter: Gradually add the dry mix to the wet, then stir in hot water or coffee until smooth.
Bake the cake: Divide batter evenly into pans. Bake for 30 minutes or until a toothpick inserted comes out clean. Cool for 10 minutes, then transfer to wire racks.
Whip the cream: Beat heavy cream and powdered sugar until stiff peaks form. Chill until ready to use.
Prepare cherries: Drain cherries and reserve syrup. Combine syrup with Kirsch (if using). Set aside some cherries for decoration.
Level the cakes using a serrated knife to remove any domed tops.
Assemble the cake: 1 Place one cake layer on a plate. 2 Brush with cherry syrup. 3 Spread whipped cream and a layer of cherries. 4 Repeat with the second cake layer.
Frost and decorate: Cover the top and sides with whipped cream. Garnish with chocolate shavings and reserved cherries.
Chill for at least 1 hour before serving for best results.