Preheat oven to 350° Fahrenheit. Line 3 5- or 6-inch cake pans with parchment paper and spray with nonstick cooking spray; set aside.
Mix cake mix, eggs, oil and milk together in a large bowl, mixing until combined.
Divide the batter between the prepared pans and bake 27-32 minutes until a toothpick inserted in the center comes out clean. Remove from the oven and let cool 10 minutes, then remove cakes from pans to a cooling rack to cool completely.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl using an electric mixer, beat the butter on medium speed for 1-2 minutes or until smooth and nearly white in appearance.
Add the powdered sugar one cup at a time, making sure to mix well after each addition. Scrape down the sides of the bowl.
Add the cocoa powder and mix until fully combined.
Add the heavy whipping cream, jam, vanilla extract, salt and a few drops of food coloring and mix on medium speed until fully combined, making sure to scrape down the sides of the bowl as needed.
Spoon some frosting into a piping bag or zipper bag and set aside for decorating.
Trim the domed tops off the cakes as needed. Place one layer of cake on a cake plate.
Using the buttercream in the bag, pipe a ring of buttercream around the edge of the bottom cake layer. Spread ½ of the jam inside the ring and spread evenly. Pipe a bit more buttercream on top of the jam and smooth out.
Top with the second layer of cake, then repeat the process.
Spread a thin crumb coat layer of buttercream over the entire cake, smoothing it out as best as possible.
Freeze the cake for 30 minutes before applying a second layer of buttercream to cover the cake.
FOR THE GANACHE:
Heat the chocolate and heavy cream in a microwave safe bowl for 30 seconds. Stir well. Continue to heat in 15 second intervals, stirring between each interval, until the chocolate is melted smooth. Allow the ganache to cool.
Make sure the cake is cool from freezing and that the ganache has cooled. Drizzle the ganache onto the center of the cake and push it towards the edges of the cake so it drips down.
Decorate the top of the cake by placing chocolate shards in the center. The heap fresh cherries, blackberries and grapes on the cake as desired.