In a heavy bottomed pot, or dutch oven, heat the olive oil and the butter, over medium high heat.

Sauté the onion until translucent (about 2 minutes).

Add the leeks and sauté until soft (about 4-5 min).

Add the potatoes and sauté with the onions and leeks for a couple of minutes. Season with salt and pepper.

Add the chicken broth and bring to a boil.

Lower the heat and simmer for 30 minutes, or until the potatoes are tender.

Using an immersion hand blender, puree the soup until smooth. Alternatively, you can work in batches using a regular blender.

Add the heavy cream and turn the heat back up to medium. Cook for about 5 minutes so it thickens a little.

Taste for seasoning and add more salt and pepper if necessary. Add a pinch of freshly grated nutmeg. Remove from heat.

Wait for the soup to cool down to room temperature and chill for at least one hour before serving (overnight is better).

Garnish with some chopped chives and serve.