Cut the leeks in half lengthwise then thinly slice them crosswise.
Heat the oil and butter in a pot over a low heat.
Wilt the leeks and celery with leaves in there until they are soft.
This will take about 10 minutes.
Add the garlic during the final 5 minutes.
Stir in the ginger and curry powder then cook for a minute over a very low heat.
Add the broth, cauliflower and lemon juice.
Turn the heat up to high and bring the soup to a boil.
Turn down the heat and simmer, partly covered, for 15 minutes or until the cauliflower is nice and tender.
Purée using the food processor until smooth, adding the Half & Half via the feed tube.
You can add extra broth now until you get the right consistency.
Season to taste with salt and black pepper.
