Make the Chocolate Cake:

1. Preheat and prepare pans: Preheat oven to 350°F (175°C). Grease three 8-inch or 9-inch round cake pans, line the bottoms with parchment paper circles, and grease the parchment. Lightly flour the pans, tapping out excess.
2. Mix dry ingredients: In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt until well combined with no lumps.
3. Combine wet ingredients: In a medium bowl, whisk together eggs, buttermilk, coffee, oil, and vanilla until smooth.
4. Make the batter: Pour wet ingredients into dry ingredients. Mix with a wooden spoon or electric mixer on low speed just until combined. The batter will be very thin – this is correct! Don’t worry, it will bake into perfect cake.
5. Bake: Divide batter evenly among the three prepared pans (about 2 cups per pan for 8-inch pans). Bake for 28-32 minutes, until a toothpick inserted in the center comes out clean and the tops spring back when lightly touched.
6. Cool: Let cakes cool in pans for 10 minutes, then turn out onto wire racks. Remove parchment paper and let cool completely before assembling, at least 1 hour.

Make the Cherry Filling:

7. Prepare cherries: Drain cherries, reserving 1 cup of the syrup. If using fresh cherries, combine pitted cherries with 1 cup water and ¼ cup sugar, simmer for 10 minutes, then strain and reserve 1 cup liquid.
8. Thicken filling: In a medium saucepan, whisk together the reserved 1 cup cherry syrup, cornstarch, and sugar. Cook over medium heat, stirring constantly, until mixture thickens and bubbles, about 5-7 minutes.
9. Add cherries: Remove from heat. Stir in drained cherries, Kirschwasser (if using), and vanilla extract. Let cool completely before using, about 30 minutes. The mixture will thicken more as it cools.

Make the Whipped Cream:

10. Whip cream: In a large bowl or stand mixer fitted with whisk attachment, combine cold heavy cream, powdered sugar, and vanilla. Beat on medium-low speed until it begins to thicken, then increase to medium-high and whip until stiff peaks form, 3-5 minutes. Don’t overbeat or it will become grainy. Refrigerate until ready to assemble.

Assemble the Cake:

11. Prepare syrup: Mix ¼ cup reserved cherry syrup with Kirschwasser (if using). Set aside for brushing layers.
12. Level cakes: If your cake layers domed during baking, use a serrated knife to carefully level them so they stack evenly.
13. First layer: Place one cake layer on your serving platter or cake board. Brush generously with cherry syrup mixture. Spread with about 1 cup whipped cream, leaving a ½-inch border around the edge. Spoon half the cherry filling over the cream, spreading gently (cherries can poke through cream).
14. Second layer: Add the second cake layer, brush with syrup, spread with 1 cup whipped cream, and top with remaining cherry filling.
15. Third layer: Add the final cake layer (place it upside-down for a flat top), and brush with remaining syrup.
16. Frost exterior: Using an offset spatula, frost the top and sides of the cake with the remaining whipped cream. You can make it rustic with visible swirls or smooth it for a clean finish.
17. Decorate: Use a vegetable peeler to create chocolate curls from the chocolate bar (slightly warm chocolate peels better). Press chocolate shavings gently onto the sides of the cake and sprinkle over the top. Arrange fresh cherries on top. If desired, pipe whipped cream rosettes around the top edge using a star tip.
18. Chill and serve: Refrigerate the cake for at least 1 hour before slicing to let it set. This cake is best served cold.