Leek and potato soup

Name: Leek and potato soup
Prep time: 10 min
Cook time: 40 min
Total time: 50 min
Cuisine: European, British
Ingredients: 350 g leeks (white part only), cut in pieces; 1 tsp salt, plus extra to taste; 30 g extra virgin olive oil; 30 g butter; 250 g potatoes, peeled, cut in pieces; 700 g water; 1 vegetable stock cube (for 0.5 l); 1 pinch ground white pepper; 1 pinch ground nutmeg; 100 g milk; fresh chives, chopped (to garnish)