The night before, soak almonds and cashews.
Lightly oil the bottom and sides of a springform pan ( I made this in a 12-inch pan, but the resulting cake isn't very tall. A 9-inch pan would be better).
Prepare the crust: place the almonds and walnuts in a food processor, and pulse until the mixture is very crumbly. Add the rest of the crust ingredients, and process until the mixture can be formed into balls that stick together. Line the prepared springform pan with the mixture, forming the bottom of the cake. This can rest in the fridge or freezer for a couple of days, or you can proceed ahead.
Prepare the filling: process the filling ingredients until they are very, very smooth (can be a while, depending on your food processor, or high-powered blender). Pour mixture over crust and distribute evenly.
Cover the pan with foil and let rest in the freezer for at least 3 hours, or overnight.
To prepare sauce, puree all sauce ingredients in a blender. Taste, and add more water if you want a more liquid consistency.
Spoon the sauce on each slice right before serving, if desired, or if eating the whole cake in one sitting, decorate the cake with the sauce and let rest in the fridge for a couple of hours before cutting. When ready to serve, remove the cake from the freezer for 30 minutes to one hour, to soften before cutting.
