In a high speed blender, blend the walnuts and cacao powder until fine.
Add the dates and blend again until the dates are broken down and the mixture starts clumping together. (Note: add a small amount of water if it's not sticking together).
Reserve some of this base mixture to make balls for the cake topping, and press the rest of the mixture into the bottom of a small springform cake pan (approximately 5 inches diameter).
Clean out the blender and add all the filling ingredients, and blend until smooth and creamy.
Pour the filling into the cake pan.
Place the cake into the freezer for about 1-2 hours.
Meanwhile, prepare the chocolate balls for the topping by rolling the reserved base mixture into balls.
Remove cake from freezer and decorate as desired.
Return to freezer for another 2-3 hours, or until the filling is solid.