Try this once and you’ll be addicted. The key to this delicacy is to buy the sirloin from a very good butcher no earlier than the day before you want to use it, so it's at its absolute freshest.
1 pound sirloin steak, trimmed of excess fat
Cut the beef into chunks and pulse in a food processor until just ground. Transfer to a large bowl. Add all the ingredients through the Worcestershire sauce, stirring as gently as possible to avoid turning the meat into mush. Add salt and pepper to taste.
The tartare can be mixed 4 hours ahead (no more than that) and kept covered and refrigerated.