Sweet potato and leek soup

Sweet potato and leek soup Recipe:

Cube leeks and sweet potato. Melt butter and add oil – lightly fry leeks for five minutes, add sweet potato and fry for a few minutes
Add enough water to just about cover the sweet potato and boil for 25 minutes or until the potato is soft.
Take off the heat and blend.
Best served at room temperature with a swirl of sour or normal cream, a squeeze of lemon and a pinch of coriander

Ingredients:

6 medium sized leeks
3 biggish sweet potatoes
30g unsalted butter
2 tablespoons olive oil
250 ml organic cream or sour cream (Clover sour cream and cream
contains stabilizer – not sure if this is allowed!)
1-2 lemons