Puree the oats, oil, syrup, cashew butter and salt in a blender. Spread the mixture over the bottom of the prepared tin and press down firmly with the base of a glass, freeze for approx. 30 mins.
Puree the cocoa butter in a blender along with all the other ingredients up to and including the lemon juice, spread over the base, freeze for a further 30 mins.
Place the chocolate in a bowl. Heat the coconut milk in a pan, pour over the chocolate, leave to stand for approx. 2 mins., stir carefully until smooth. Pour the chocolate mixture over the blackberry layer. Cover and chill for approx. 2 hrs.