Either way, they popped into my mind again when trying to decide what to make for the weekend. I wanted something that would get me through the start of the week too, when I don't have time to bake. These seemed ideal as the 30 x 20cm traybake cuts into around 24 pieces. I use a baking tin that is slightly smaller than specified in the American recipe (8 x 12" instead of 9 x 13") as that's the size of tray I have; I think standard sizes are slightly different in the USA. I added another 5 minutes to the baking time to compensate for a deeper mixture.
this blog post I've 'translated' the cup volumes to metric weights, with 150g of chocolate going into the bars, and 200g being used for the topping.
Unfortunately, I must have covered the bars before they were completely cold - when I went back the next morning to photograph them, the top was covered with little pock marks, which I can only assume was condensation dripping from the aluminium foil covering the tray overnight. It didn't affect the flavour, but did spoil the photos a bit.