Line two 9'13 cake pans with parchment paper cut to overlap the sides of the pan, then set aside. In two large mixing bowls pour one box of White cake mix into each. Cut one package of extra-fine baking marzipan into small pieces for one of the cakes, then cut the other package of baking marzipan into small pieces, to combine with the other cake. With a pastry cutter, cut in the marzipan into each bowl of white cake mix. You want it to be well-incorporated, and form little crumbs with the mix. Now add the water and any other ingredients the cake mix calls for. Use an electric mixer to incorporate the marzipan into the batter thoroughly, then start with the red food color.
With a long spoon, stir in the red liquid food color and keep swirling it in till you reach the desired shade. Do the same for the green food color in the other bowl. Then carefully pour the batter from one bowl into one of the parchment-lined cake pans, vice-versa. You now have a red cake and a green cake ready to bake in a pre-heated 350F oven. The cakes bake for 20-30 min, or till a toothpick comes out clear. Let the cakes cool thoroughly in the pan for 15 min, then lift the parchment paper out of the pan and let the cakes cool on two separate cookie sheets for a couple of hours.
Once cooled, with a long serrated knife, still on the parchment paper, cut each cake into thirds, 3 long logs. You should now have 3 green logs of cake, and 3 red logs sitting on the original parchment paper used during baking. Line two more cookie sheets with plastic wrap. Then, take a red log from the parchment paper, with a long knife and sliver it off the parchment, and onto the plastic wrap. Now, with a regular knife, swirl the raspberry preserves on only the top the red log, making a somewhat thin, but substantial layer of filling.
With a serrated knife, then take a green log from the parchment paper, and place it right on top of the red log with preserves, on the plastic wrap. Swirl on preserves on top of the green log. Now another red log gets moved from the parchment paper and placed on top of the other two logs that are on plastic wrap, so you should now have a stack of red-green-red cake logs with raspberry preserves in between only the middle layers. At this point, wrap the top part of the stacked 3 logs in plastic wrap and put in the refrigerator to set. You can weight it down with plates to really set the layers.
Repeat the steps in the above paragraph with the remaining logs of cake. In this case, you should end up with green-red-green, as the logs are transferred, with a long serrated knife, from parchment to plastic and the middle layers are filled with raspberry preserves. This stack is also put into the refrigerator, and weighted down with plates to thoroughly set the layers.
While the logs are setting in the refrigerator, make a Chocolate buttercream frosting to top the stacked logs with. Melt the chocolate bars in a fry pan sitting on a pot of lightly simmering water. In another pan, melt the butter, but don't let it burn. Take the butter off the heat, and whisk in powdered sugar to the melted butter. Add in 1 cup of heavy whipping cream still whisking by hand. Once reasonably incorporated, add the butter/sugar/whipping cream mixture to the sufficiently melted chocolate and stir gently by hand. Swirl it till well-incorporated. Once thoroughly mixed together, to make a frosting, let it cool at room temperature for about 40 minutes.
Once the frosting has cooled to room temperature, remove the stacked logs from the refrigerator and, still on the plastic wrap, frost all 5 sides of the one of the 3 stacked cake logs, then frost the other stack of 3 cake logs on all 5 sides. Lightly pull the plastic wrap up over the newly frosted stacks and let sit in the refrigerator till ready to serve. When ready to serve, cut into bread like slices, length-wise.