Harissa beef sirloin with pepper and lemon sauce

This is a great dish to feed friends, if you like knowing that all the work which needs doing is done well before anyone arrives. The pepper sauce can be made a day ahead. You can also marinate the meat for a day and it can be seared in advance too. Keep separate in the fridge, and bring everything back to room temperature before serving or cooking and the meal can be on the table 15 minutes after the stove goes on. This works well with the oven-roasted chips