On my third attempt at the recipe, I think I’m getting close. This time I used 200g flour, 75g warm milk, 50g butter and 1.25g each of salt, sugar and yeast. That gave a fairly stiff but workable dough. I rolled it out with my pasta machine (the widest setting, probably about 2mm, was sufficient) and didn’t skimp on pricking holes. I also set the fan oven to 150°C.
After about 15 minutes, including a tray rotation part way through, they had risen a bit but had only just begun to pick up some colour. I took them out at that point and cooled them. They still seemed a bit bready in the middle so, after baking something else, I put them back after turning off the oven and, with the door cracked open, let them dry out further.
I haven’t quite recreated the biscuits I remember but I’m much, much closer after a few iterations and, if nothing else, I’ve come up with a result that will prove to work well with port and stilton!