This is a good way to stretch a couple of sirloin or rump steaks out into four snacks or light lunches, or you could even serve them as starters.
I use a ribbed griddle pan at home for the steak, then cook the bread in the same pan while the steak is resting, so you get a deliciously-flavoured bread, rather than just toasting it. If you can find mustard made with grape must (try specialist food shops and delis), it works brilliantly on the bread once it has been grilled. Otherwise, use Dijon or grain mustard.
4 medium or 2 large red onions
2 sirloin or rump steaks, weighing about 200-250g each
Salt and freshly ground black pepper
A little vegetable or corn oil for brushing
4 slices of bread cut about 1½cm thick
2tbsp grape must mustard or Dijon or grain mustard
A handful of watercress with the woody ends removed
2tbsp olive oil
½tbsp red wine vinegar
Preheat the oven to 200C/gas mark 6. Wrap the onions in foil and bake for about 45 minutes or until soft. Remove the foil, leave to cool, then remove the skin and cut into quarters and separate the natural layers.
Preheat a ribbed griddle or barbecue. Season the steak, lightly brush with oil and cook for 3-4 minutes on each side, then transfer to a plate and leave to rest for a couple of minutes.
Griddle the bread on both sides until crisp; spread with the mustard.
Slice up the steak, arrange on the bread with the onions and watercress leaves, then mix the olive oil with the red wine vinegar and any juices from the steak and spoon over the sandwiches.