The following recipe comes from the Nosher via My Jewish Learning:
2 Tbsp vegetable oil
2 medium onions, chopped (or use one large leek plus one onion)
2 lbs all-purpose potatoes, peeled and coarsely chopped
6 cups vegetable stock
salt and freshly ground black pepper to taste
1/8 tsp freshly ground nutmeg
3/4 cup cream
1 Tbsp chopped fresh chives, optional
6-8 shiitake mushrooms, optional
2 tsp vegetable oil, optional
dairy sour cream, optional
Heat the vegetable oil in a soup pot over medium heat. Add the onions and cook, stirring occasionally, for 2-3 minutes.
Add the potatoes, stir for a minute. Pour in the vegetable stock. Add salt and pepper and the nutmeg. Bring to a simmer, lower the heat and cook, partially covered, for 45 minutes or until the potatoes are tender.
Meanwhile, roast the mushrooms. Preheat the oven to 450 degrees. Rinse and dry the mushrooms and coat them with the 2 tsp vegetable oil. Place on a baking sheet and roast for about 25 minutes or until well browned. Chop or shred to be sprinkled over the soup.
Take soup off the heat and let cool slightly. Puree the ingredients in a blender or food processor or with an immersion blender. Return the soup to the pan. Add the cream and heat through. If desired, serve with a garnish of chopped chives or chopped, roasted shiitake mushrooms. Add a dollop of sour cream if desired.