To prepare the chocolate layer, bring the cream gently to the boil in a medium pan on a medium heat.
Meanwhile, snap the chocolate into a large jug.
Remove the cream from the heat once it reaches the boil and pour over the chocolate.
Stir until melted to a smooth, rich sauce, then leave to cool to body temperature.
Meanwhile, oil the loaf tin and line with parchment paper.
Stir the nuts through the salted caramel sauce and then pour into the base of the tin, spreading it evenly with the back of a spoon.
Pour the cooled chocolate mixture on top, cover with cling film and refrigerate for at least 4 hours or overnight, until set firm.
This can be made up to 24 hours in advance and left in the fridge.
Just before you want to serve, lay a long serving board upside down over the tin and turn both over together, allowing the terrine to drop out.
Remove the tin and peel off the paper to reveal the turtleback.
Leave to come to room temperature for 15-20 minutes before serving.
Dipping your knife in boiling water and wiping dry between every slice, cut into 12 slices, serving 2 per person.