So what you'll need is as follows:
- 30-40 Oreos - available in the UK in packets of 14 or so, so three packets will probably do you. Alternatively you could assert your Britishness and use Bourbons or something instead;
- one standard 250g pack of butter;
- 120g brown sugar;
- one 300ml carton of double cream;
- 350g dark chocolate.
Step one is to make a biscuit base., much the same as if you were making cheesecake, by blitzing the Oreos, filling and all, in a food processor and then stirring in half the butter, melted. Then press this into a flan tin and put it in the fridge for an hour or so.
Step two is to make some caramel. This sounds like the sort of scary baking chemistry that requires jam thermometers and the like, but actually it couldn't be easier. Throw equal 120g quantities of butter and brown sugar into a saucepan, stir till the sugar has dissolved and the whole thing is bubbling (no more than five minutes or so), then take the whole thing off the heat and stir in 60ml of the double cream. Set this aside for 10-15 minutes to cool, then pour it into the crust - you shouldn't have to do any spreading as it should still be liquid enough to find its own level. Stick it back in the fridge for half an hour or so.
Step three is to make some chocolate ganache. Again, this all sounds a bit like a job for Lindt's master chocolatiers, but it's actually pretty easy. Smash up some dark chocolate into small pieces, heat up the rest (240ml) of the cream in a small saucepan, and pour it over the chocolate in a bowl. Now in theory the heat of the cream should melt the chocolate, but you may find that you have to apply some extra heat to get it to mix smoothly, particularly if you've used (as I did) a very high-cocoa content chocolate. Then pour the whole shebang into the flan tin on top of the caramel and put it back in a the fridge for an hour or two. You may find that some of the fat in the chocolate separates into a buttery deposit on top of the tart as it solidifies; you can just scrape this off with a knife and discard it.
This makes a phenomenally rich chocolatey tart that the original recipe recommends garnishing with some sea salt. I think this is an excellent idea, but it perhaps won't be for everyone. If you find the whole thing a bit overpowering then you could increase the proportion of cream in the ganache or use a lower-cocoa-content chocolate. Also, cut smaller slices than you think you'll need, it's really rich.
In a way it's a sort of upside-down version of this earlier largely improvised creation.