To make the olive oil pastry base
Preheat the oven to 180°C (fan assisted 160°C)/350°F (320°F fan assisted)/gas mark 4 (gas mark 3 fan assisted).
Mix all the ingredients together to form a dough.
Place the dough between 2 sheets of baking paper and roll until 1 mm thick.
Refrigerate for 30 minutes.
Put onto a baking tray and bake until just crisp.
Remove from the oven and, whilst still hot, press a 20 cm x 15 cm mould on top and push down hard to cut out.
Place the chocolate in a bain marie and melt gently.
Spread the chocolate evenly over the pastry base making sure any holes or gaps are fully filled.
To make the topping
Place the chocolate and salt into an electric mixing bowl fitted with a whisk attachment.
Put the sugar into a heavy based, small saucepan and gently melt to a dark caramel.
Add the water and simmer gently until the sugar has melted.
Weigh 250 g of the boiling caramel stock and pour over the chocolate and salt.
Whisk on the lowest speed until the temperature has reduced to 35°C/95°F.
Pour the mix onto the prepared base and put in the fridge for 4 hours to set.
Cut into thin slices and serve with a zesty sorbet like raspberry.