Step 1: Make the Chocolate Sponge Cake

1. Preheat the oven to 350°F (175°C). Grease and line a 9×13-inch baking pan.
2. In a bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
3. In another bowl, beat butter and sugar until fluffy. Add eggs one at a time, followed by vanilla extract.
4. Alternate adding dry ingredients and buttermilk, mixing until smooth.
5. Pour the batter into the pan and bake for 25-30 minutes, or until a toothpick inserted comes out clean.
6. Let the cake cool completely, then slice it into two equal layers.

Step 2: Make the Cherry Filling

1. In a saucepan, cook cherries, sugar, and cherry liqueur over medium heat until softened.
2. Stir in the cornstarch mixture and cook until thickened. Let cool.

Step 3: Prepare the Whipped Cream

1. Beat heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Step 4: Assemble the Cake

1. Place one cake layer on a serving plate. Spread half of the whipped cream over it.
2. Spoon the cherry filling evenly over the whipped cream.
3. Place the second cake layer on top and spread the remaining whipped cream.
4. Garnish with chocolate shavings, fresh cherries, and chocolate drizzle.