1. You'll need your choice of crusty loaf, a couple of good steaks - I used rib-eyes - roughly the same shape in plan as the loaf plus 500g of mushrooms and 200g of shallots.
2. Slice off the top quarter of the loaf, hook out most of the crumb and save for breadcrumbs.
3. Cut your shallots and mushrooms into fine dice and put about 75g of butter into the pan. Other fats will do. I got lucky, Allegra McEvedy had used my kitchen for a shoot the week before and had left just the right quantity of beef bone marrow in the fridge.
4. Cook mushrooms and shallots fiercely in the butter, stirring continuously, until they've softened, reduced in size and lost a substantial amount of moisture. This is the classic 'duxelles' mixture used in a beef Wellington. Some have suggested that whole portabella mushrooms and sliced onions could be substituted but that feels like a vegetarian option to me and somehow undermines the whole point.
5. Once sufficiently cooked down the mushrooms will absorb flavour like a sponge. I used plenty of salt and black pepper, some finely grated garlic a shot of brandy and a splash of Worcestershire sauce. Those fearing scurvy might add some chopped parsley too.
6. Season your steaks and bring them to the pink side of medium in a searing hot dry pan. Don't bother resting them. Work fast and tuck the first one, dripping and hot, straight into the bottom of the hollow loaf. It doesn't matter if the juices leak now - in fact it just makes the whole thing more sublime.
7. Dollop in your hot mushroom mixture and tuck your second steak over the top. At this stage I usually smear hot horseradish on the top steak and Dijon mustard on the inside of the lid before fitting it back on to the loaf.
8. Wrap the whole thing in greaseproof paper and tie with butcher's string, then wrap in two layers of foil and smush flat under a heavy cutting board and as many weights as you can find. Leave under the weights in a reasonably cool place (don't refrigerate) for at least six hours or preferably overnight. Remove the foil and cut through string, paper and sandwich.