Carrot and coriander soup

1 medium onion, finely chopped

6-8 medium carrots, peeled and finely chopped

1 stick of celery, finely chopped

1 clove of garlic, crushed

1 litre of good vegetable stock

1 tsp ground coriander

Sea salt and black pepper

80g butter

Vegetable oil

Crème Fraiche to serve