1. Slice a lid off the top of the loaf and scoop out most of the bread inside, leaving a centimetre or so around the crusts.
2. On a frying pan on a really high (smoking) heat, season then quickly (30 seconds each) fry the steaks on both sides to your taste and put straight in the loaf.
3. Meanwhile, season the red onions until nearly caramelised and add the oyster mushrooms, then cook until soft.
4. Slice the cheese and place on top. Gently fry the chard (removing the stalks first) in some butter until wilted then place on top.
5. Smother the bread lid in the mustard and mayonnaise then put back on.
6. Finally, wrap the whole thing up tightly with greaseproof paper and string and squash between two chopping boards, or even between heavy books or under sofa cushions, and leave unrefrigerated for approximately six hours.
7. To serve just slice like a pie