Creamy Mustard Chicken with Cabbage

1 large leek - sliced
1/4 large savoy cabbage - chopped
1tbls butter
salt and pepper
2 chicken breast fillets - chopped
1-2 tbls wholegrain mustard
300ml whipping cream

Preheat oven to 180c
Melt butter in pan, add leek and cook for 1 min.
Add cabbage and cook for 1 min
Season with salt and pepper
Transfer into oven proof dish
Arrange chicken on top of cabbage. 
Combine mustard and cream and pour over chicken and cook for 20-30 mins till chicken is cooked.