Celery should have crisp long stems attached to a sound base and the leaves should be vibrant and green. It should have tightly packed, firm heads with no brown patches on the outer layers.

Add a 100g bag rocket, 1⁄2 finely chopped celery head and 50g chopped walnuts. Combine olive oil, Dijon mustard and white wine vinegar in a bowl and give a good mix with a whisk or fork to combine.