You can juice it or use it in salads (but chopped thinly) or in a quiche. You can also wash the leaves, dry them very well (not a single drop of water left), remove the stern,  then rub the green leaves very well with olive oil, put some salt and put them in the oven at 175C for about 10 to 15 minutes (until the edges start becoming brown). Enjoy! More info here

How to store it?