Pour the olive oil into a small pot and heat on the stove. Add the drained capers to the oil and flash fry for about 30 seconds to a minute, until the capers pop and open up. Drain the oil from the capers on a kitchen towel.
Roll the fillet into a cylinder and tie with string, then roll in freshly ground salt and pepper and rub with the wholegrain mustard. Flash fry the fillet in the olive oil in a hot pan, then rest. Remove the string, wrap in cling film and store the rolled fillet in the freezer until required. When ready to serve, remove the fillet and slice it into very thin rounds with a serrated knife. Arrange on a large dinner plate, scatter with the flash fried capers, drizzle with the lemon juice and extra olive oil, and arrange the pecorino shavings and rocket over the carpaccio. Finish off with a last grinding of fresh black pepper and sea salt.
