Preheat oven to 350°F. Spray and line bottoms two 8 or 9 inch cake pans with parchment paper.
Sift together flour, cocoa powder, baking soda, salt, and pudding mix. Set aside.
In a stand mixer cream butter and sugar for 2 minutes. Add vanilla. Add eggs one at a time and mix until completely incorporated.
Alternating between flour mixture and buttermilk (or whole milk), add to mixer in two batches, starting with flour and ending with buttermilk. Mix on medium speed until smooth and fully combined, scraping sides if needed.
Divide batter evenly between cake pans.
Bake on center rack for 25-30 minutes or until a toothpick inserted in the center comes out clean and the tops spring back when lightly touched.
Let cool in pans for 5 minutes, then flip out onto a cooling rack and remove parchment paper.
For the Cherry Syrup
In a small bowl, mix together the cherry preserves and water until a thin consistency. Add more water if needed. You can also use Cherry Kirsch if you prefer to give your cake a little "kick".
While still hot, brush top of cakes with cherry syrup. Set aside to cool.
For the Whip Cream
In the bowl of a stand mixer fitted with the whisk attachment, mix whipping cream and sugar. Beat on high until thick (about 4 minutes).
Put in refrigerator and keep cold until ready to use.
Now assemble the cake. On a cake plate place first cake layer with syrup side up.
Spread half of the whip cream over the cake and then place second layer of cake on top and spread remaining whip cream on top.
Place in the refrigerator to keep cool while making ganache.
For the Chocolate Ganache
Finely chop chocolate bar and place in a bowl (or use chocolate chips).
Using the microwave heat whipping cream until hot, about 1 ½ minutes, being careful not to scorch.
Pour hot milk on top of the chocolate, let it set for about 3 minutes and then stir until smooth.
Allow to cool for 10-15 minutes so not hot but still spreadable.
Take cake out of refrigerator and slowly pour ganache over the top, covering sides completely.
Place back in refrigerator to set ganache and then take out when ready to serve.
Decorate with cherries, whip cream, cocoa powder, or chocolate curls.
Notes
Cakes can be stored in the refrigerator for 3 days or in the freezer for up to 3 months when tightly wrapped in saran wrap.