Cut off the top and bottom parts of the leeks, slice them in half lengthwise, and rinse them with water to remove dirt between the layers.
Slice the leeks and onion thinly.
In a large pot, warm up the olive oil, add the chopped leeksandonions, and fry them for 5 minutes, stirring often.
Add peeled and chopped potatoes, vegetablebroth, bayleaf, thymeleaves plucked off the stem, salt, blackpepper, and gratednutmeg.
Cover with a lid, bring to a boil, then crack the top open, and simmer on medium-low heat until the potatoes are fork-tender (about 15-20 minutes).
Turn the heat off and blend the soup with an immersion blender (or in batches with a regular blender) until you reach your desired texture.
Stir in the greek yogurt.
Taste and adjust for salt and pepper, and add more broth if you like a thinner soup.
Serve in a bowl with a drizzle of good quality extra virgin olive oil, freshly ground black pepper, chopped chives, and a slice of toasted artisanal bread brushed with garlic.