Mache or Valerianella locusta

Commonly known as lamb's lettuce. It is a french winter salad green, as testified by the fact that it has self-seeded now following a crop last year. It's very delicious and nutty and hard to find here.

It's come up quite thickly too, which again testifies to it's other common name - corn weed as it apparently comes up as a weed (as if!) in cornfields. How could it be a weed? Just harvest and eat!