Prepare the leeks: Trim and discard the roots and dark green ends of the leeks so that only the light green and white parts remain. Cut each leek in half lengthwise and slice thinly into half moons. Transfer to a bowl and fill with cool water, and use your hands to stir and separate the leeks (the outer layers can be quite sandy and dirty.) Strain through a colander, rinse, and drain. Set aside.

Melt the butter in a large pot over medium heat. Add the celery, onions, and leeks, and season with salt and pepper. Cook, stirring occasionally, until the onions are translucent and the leeks have softened, about 15 mins.

Add the stock, potatoes, thyme, bay leaf, and nutmeg. Increase the heat to high and bring to a boil, then reduce to a simmer over medium heat. Cook until the potatoes are just tender when pierced with a fork,( not cracking and falling apart), about 9-10 minutes. Turn off the heat.

Remove thyme sprigs and bay leaf, and purée the soup with an immersion blender until smooth. (If you don’t have an immersion blender, a regular blender can be used! Allow the soup to cool at least slightly, then transfer to the blender and blend in batches. Be sure to vent the blender when blending as steam from hot liquids can build up pressure and blow the lid off.)

Once smooth, strain the soup into a large bowl through a mesh sieve and work thru with a large spoon. Discard the pulp left in the sieve. When all the soup has been strained, stir in the cream. Serve the soup hot or cold*, topped with chives. (*For me, this soup is perfect as is when served hot. When served cold, I add around ½-1 cup of water to thin the soup slightly.)