Apparently this type of sandwich was made for the posh folk when they went out on shooting (or hunting) trips as it travels well and probably improved even more after being squashed in someone's saddle bag! Alas I have no shooting trips planned but have got the week off work so what better time to make it?!
Be warned - although this is a very simple sandwich, it does take a while to prep and is best left pressing for at least 5 hours!
To begin with you need to make the mushroom mixture - I used half chestnut mushrooms and half white closed cup mushrooms, about 14 medium sized mushrooms in total.
Finely dice the mushrooms.
I don't think it matters whether you use onions or shallots - shallots are a little more fiddly to peel and chop but I like the flavour. I finely sliced 8 shallots and then softened them in a little butter and olive oil then added some very finely sliced garlic (3 cloves).
Once the shallots have softened, add the chopped mushrooms and cook the mixture down until and excess liquid has cooked away. If there is too much moisture left in the mushrooms the sandwich will become too soggy. Season with salt and pepper to taste. I found that leaving the mushroom mix to stand allows any excess moisture to drain plus it allows you to get on with the rest of the steps!
Slice a "lid" off the top of the bread and scoop out most of the bread inside. If you get a little carried away with the scooping and feel there are any weak spots, you can patch it up with some of the bread you've taken out.
Now the steak! Cook the steak as you would normally but without oil - I like mine still pink in the middle so cooked each piece of meat for about 3 minutes on each side plus sealed around the edges. It doesn't really matter what sort of steak you choose for this sandwich but make sure it's decent quality. I chose rump.
Once the steaks are cooked, tuck them straight into the bread shell. Wait - don't I need to rest them, I hear you ask. No! You want all of those tasty juices to soak right into the bread. Make sure that you tuck the meat right in around the edges. I used one of my steaks as a "filler-in" steak so sliced smaller pieces off to fit in the gaps.
Now time for the mushroom mix. You want to make sure any little gaps around the beef are filled in so once you've spooned the mixture over the beef, push down with the back of a spoon and smooth the top. Add the rest of the steak.
For added flavour, spread either a horseradish cream or some hot mustard to the "lid" (I used horseradish) then put the lid on top of the loaf, trying to make it match up with where it was cut from.
Wrap the whole loaf tightly in greaseproof paper (I used 2 sheets to prevent any leakages) like you would a present then tie securely with string. Unfortunately I had no string to hand so had to stick the bits down with duct tape...
Time to squash! Use a baking tray (or something else flat but strong) and load up with any weights you can find around you. Not being a gym-goer I raided my cupboards for cans but you could use heavy books, dumbells, bricks....I added a few big books after a couple of hours.
This is the hard bit - you now have to leave the sandwich for hours and hours (5+ is the ideal time) or even worse - OVERNIGHT! It's worth it though - promise!
Once pressed, slice into wedges and serve however you like - with a salad, some relish or chutney or just on its own!