For the base
2 x 154g/5½oz packets chocolate cookies, such as Oreos or Bourbons(28 small biscuits in all)
50g/1¾oz dark chocolate (min. 70% cocoa solids)
50g/1¾oz unsalted butter, softened
½ tsp smoked sea salt flakes (see tip section)
For the filling
100g/3½oz dark chocolate (minimum 70% cocoa solids)
25g/1oz cornflour
4 tbsp full-fat milk
500ml/18fl oz double cream
50g/1¾oz cocoa powder, sieved
2 tsp instant espresso powder or strong instant coffee powder
75g/2½oz caster sugar
1 tsp vanilla paste or extract
2 tsp extra-virgin olive oil
¾ tsp smoked sea salt flakes
Method
For the base, snap the biscuits into pieces and drop them into the bowl of a food processor. Do likewise with the chocolate, then blitz them together until you have crumbs. Add the butter and salt, and blitz again until the mixture starts to clump together. If you’re doing this by hand, bash the biscuits in a freezer bag until they form crumbs, finely chop the chocolate and melt the butter, then mix everything, along with the salt, in a large bowl with a wooden spoon or your hands encased in disposable vinyl gloves.
Press into your tart tin and pat down on the bottom and up the sides of the tin with your hands or the back of a spoon, so that the base and sides are evenly lined and smooth. Put into the fridge to harden for at least 1 hour, or 2 hours if your fridge is stacked. I wouldn’t keep it for longer than a day like this as the crust tends to get too crumbly.
For the filling, finely chop the chocolate. Put the cornflour into a cup and whisk in the milk until smooth. (I find it easier to use cups for the liquids – in which case the milk measure is equivalent to an American quarter cup, and you’ll need 2 cups of cream.)
Pour the cream into a heavy-based saucepan into which all the ingredients can fit and be stirred without splashing out of the pan, then add the finely chopped rubble of chocolate, the sieved cocoa (or just sieve it straight in), espresso or instant coffee powder, sugar, vanilla paste or extract, olive oil and smoked salt. Place over a medium to low heat and whisk gently – I use a very small whisk for this, as I’m not aiming to get air in the mixture, I’m just trying to banish any lumpiness – as the cream heats and the chocolate starts melting…
