Place all the ingredients in the blender and blend for 30 seconds. Let the mixture cool in the fridge at least 1 hour before using.
Over medium heat coat the crepes pan with some butter until it begins to sizzle. Pour an amount equal to approx 2 tablespoons of the mixture in the pan and moving rotate the pan to spread evenly. Cook the crepe until the edges curl up, then flip and cook for a few more seconds. Set the crepes aside to cool and keep cooking the crepes until the batter is over.
Place the semi sweet chocolate in a heatproof bowl. In the meantime bring to a boil the heavy cream on the stove over medium heat. Pour the cream and stir to melt the chocolate, and then add the gran marnier.
Let the mixture cool to room temperature, mixing from time to time. When the mixture is cool, whip it until lighter in color.
Place the eggs, sugar and gran marnier in a heatproof bowl and beat them with a mixer until light yellow (10 minutes). In the meantime bring water to a boil in a sauce pot over medium heat. Place the heatproof bowl of the sauce pot and stir to cook the zabaione for 3 minutes until it turns golden. Set aside and bring to room temperature
In the meantime beat the heavy cream to soft peaks and fold in the cool zabaione.
To assemble the cake
Place the first crepe on a cake stand and with a spatula spread some of the ganache cream. Cover with another crepe and some zabaione cream. Keep alternating the creams until you have approximately 7 layers per color. Place the remaining creams in pastry bags and decorate the top of the cake with the 2 colors.