Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. In a large bowl, beat 6 oz of unsalted butter with 4.75 oz of granulated sugar and 5 oz of brown sugar until light and fluffy, around 3-4 minutes.

In a separate bowl, mix 2 large eggs, 2 tsp of vanilla extract, 8 oz of buttermilk, 4 oz of sour cream, and 2 tbsp of water or brewed coffee until well combined. Gradually incorporate this mixture into the beaten butter and sugar.

Sift together 7.8 oz of all-purpose flour, 3 oz of unsweetened cocoa powder, 1.5 tsp of baking soda, and 0.5 tsp of salt in another bowl. Slowly add this sifted mixture to the wet ingredients.

Pour the combined batter onto the prepared baking sheet and bake for 15-18 minutes, until a toothpick comes out clean. Allow to cool completely on a wire rack.

While the cake cools, prepare the kirsch syrup by combining 0.5 cup of granulated sugar and 0.5 cup of water over medium heat until dissolved, then stir in 2 tbsp of kirsch or 1-2 tsp of cherry extract.

Whisk together 4 large egg yolks and 3 tbsp of cornstarch in a bowl. Heat 2 cups of milk until simmering, then gradually whisk into the yolk mixture and return to heat, thickening. Fold in 6 oz of melted semi-sweet chocolate and 2 tbsp of unsalted butter.

Once the cake is cooled, use a round cutter to cut rounds. Brush each round with kirsch syrup, add chocolate pastry cream, and fresh cherries. Stack rounds and chill for at least 30 minutes.

After chilling, spread pastry cream on top of each mini cake, sprinkle chocolate shavings, pipe whipped cream rosettes, and add a fresh cherry for garnish.