Preheat the oven to 190C.
Wash the leeks. Use only the white part (keep the green part for a vegetable soup).
Cut the white stalks in half and carefully rinse with cold running water. Remove all trace of sand or earth.
Cut each stalk into 5 pieces.
Bring the chicken stock to a boil then let it cool.
Whisk in the cream and mustard.
Par boil the leeks for 3 minutes in salted water.
Stop the cooking by rinsing them under cold water.
Divide the leeks between 4 cocottes.
Pour several spoonfuls of the mustard and cream mixture over the top of each one.
Bake for 20 minutes.
Serve hot and bubbly!
