I generally don't add cream (although I did to make the serving looks fancy above). Feel free to though, I know a lot of people do.
3 leeks, well washed and chopped
5 potatoes, peeled and chopped
1 litre of stock (chicken or vegetable)
1 tbsp butter
small splash of olive oil
salt and pepper
1 tsp nutmeg
Melt the butter and the oil together in a large pot and fry off the leeks on a low heat for 10 - 15 minutes until very soft.
Add the potatoes and fry for a further few minutes.
Add the stock with the nutmeg, salt and pepper.
Bring to the boil and allow to simmer for 20 - 30 minutes.
Some people prefer this soup like this, so feel free to serve now. I prefer it pureed.
Serve with bread and cream if desired.