1) Line the bottom of a round cake pan with parchment paper. Butter it or spray with a non-stick baking spray.
2) Break the chocolate into small pieces. Place the semi-sweet or milk chocolate in one bowl and the white chocolate in another. Add 4 tablespoons of butter to each. Stand the bowls over pans of hot water until the chocolate and butter have melted, stirring occasionally, or melt them in a microwave oven. Place the bowls on the counter and stir half the cream, nuts, dates and crushed cookies into each.
3) Spoon the darker chocolate mixture into the pan and spread level with the back of a spoon, pushing the mixture down into the corners. Top with the white chocolate mixture. Cover with foil or plastic wrap and chill until set. Remove from the pan and serve cut into slices.