Try Medania
From March to July sow thinly about 1cm (1/2in) deep in rows 30cm (12in) apart and water well. As the seedlings start to grow, remove the weaker ones (thinning) to leave one every 5cm or so. The seedlings you remove can be used in salads. Keep well-watered in dry weather.
Once the plant has developed harvest just as many leaves as you need and leave the rest on the plant.