The first attempt went quite well but I wasn't entirely happy with the biscuit. Whilst the olive oil biscuit base might work very well in the context of one of Heston's menus it's not quite right for just scoffing. The quick shortbread I used for the Public sector version didn't really cut it either.
Times published (which I found by a bunch of people complaining that the Dulce de leche step took 3 hours) for a simplified version. I used the short bread from that which worked out quite well (that's it to the left) and had much more of the texture that I associate with Millionaire's shortbread/caramel squares.
The salted butter caramel from the FatDuck cookbook was really good, I'd had a couple of issues with it, that I was hoping to resolve with the purchase of a sugar thermometer and an untextured pan. Whilst it worked better than before (and seems to have created a very rich sticky caramel) I still had issues with it sticking & singeing.
Once again rolling it out & cutting to size was very tricky, hopefully The big fat undertaking will be making the full recipe before too long (though I think the chocolate wine may require a centrifuge) and I'll have another source of reference. The tempered chocolate though is definitely a step not to miss out, there are several easy ways to do this at home, that don't involve water baths or marble slabs and the end product is glossy chocolate with a real snap.
Assembling the squares isn't to bad. This time round I'd decided to make one giant piece & then cut it to size, which makes working with the sticky slab of caramel easier, but means you have to have a bowl of hot water handy to slice the chocolate layer.
I've tasted the trimmings and its pretty much close to my ideal of Millionaire's shortbread, a crumbly base, sticky caramel and an intense chocolate hit. Given the richness of the caramel (it uses both butter & double cream) you have to be a bit careful with the base (I crossed off one recipe that used 500g of butter) and its best to use a high cocoa dark chocolate for the top (otherwise I think it could get too cloying).
I might have a go at the Dulce version in the future, but to be honest I'm quite happy to go to the trouble of making the caramel & tempering the chocolate.