Cut the leeks into 10cm lengths, washing out any grit
Add the leeks and oil into a saucepan, making sure the leeks can all sit comfortably in a single layer.
Sautee the leeks for a few minutes.
Add the tarragon on top of the leeks, & clamp the lid down on the saucepan. This will ensure the leeks steam in their own juices, softening their insides and caramelising the outer leaves.
Serve with a sprinkle of extra tarragon & a smidge of salt.