I'm not a cake decorator type, but I did come up with this cake that impressed my family for my son's birthday that incorporated his requested ingredients. Couldn't find a marble cake mix, so I found online that you could use any yellow cake mix, reserve 3/4 cup batter and mix in with 2 tablespoons cocoa.. Dab in about 5 places on top of cake batter that you have poured into pans. Using a table knife, gently pull chocolate through batter. Do not sitr.
I used Nutella straight out of the jar for the frosting. I prefer a less sweet cake, so didn't frost sides.
Sprinkled chopped hazel nuts over top.
Sprinkled Heath bar pieces I found in grocery baking aisle next to the chocolate chips on spoonfuls of Nutella to decorate around cake bottom.
Used this Raspberry Goo recipe as filling between layers. Reserved a few nice looking berries to garnish top and drizzled remaining goo over individual cake pieces when serving:
2 cups fresh raspberries
2 Tablespoons agave syrup
2 Tablespoons coconut butter or oil
1 teaspoon lemon juice.
Place all in food processor or blender and pulse until consistency of your likng.