Lovage and potato soup

2 tsp unsalted butter
1 cup thinly sliced leeks, or two onions, chopped
100g potatoes, peeled and sliced 1/4 inch thick
4 cups chicken stock
2 cups water
1 cup loosely packed lovage leaves, chopped
salt and freshly ground pepper to taste

Melt the butter in a soup pot.
Add the leeks or onion and saute at a fairly low heat until very soft and beginning to brown, which could take up to twenty minutes, probably less for leeks.

Add the potato slices and stock.
Simmer the soup, uncovered, until the potatoes are very soft, 20 to 30 minutes.
With a wire whisk, gently whisk the potatoes to break them up (how much is up to you).
Now add the chopped lovage leaves and simmer until they are tender.
Smaller, younger leaves take less time than larger, older leaves, so how long this will take is variable.
Add salt and pepper to taste, and serve.