A play on the classic vitello tonnato, this beef tagliata with tonnato sauce keeps many of the same ideas from the original. However, instead of poaching a piece of veal, I’ve chosen beef in the form of sirloin steaks, which are more readily available. The tonnato sauce – salty, briny and fresh – is a quick concoction that really works here, drizzled over the steak nestled among peppery rocket leaves and parmigiano reggiano.