Seal the sirloin all over including the ends. Set aside in the roasting tin. Preheat the oven to 220C/200C Fan/Gas 7. Meanwhile mix together the mustard, salt and pepper and rub all over the sirloin.
quick-pickled in a vinaigrette of white wine vinegar, salt and extra virgin olive oil, then tossed with baby cos leaves. I used sirloin for this but any steak will be good.