Adapted From Dishing Up The Dirt
2 tablespoons olive oil
2 medium leeks (or one large), diced, white and light green parts only
1 small yellow onion, peeled and finely chopped
2 cloves of garlic, minced
1 medium-sized celeriac, peeled and cut into 1 inch cubes
2 yukon gold potatoes, peeled and cut into 1 inch cubes
Hefty pinch of salt
4 cups vegetable stock (plus more to thin as needed)
1 tablespoon fresh lemon juice
Crème Fraîche, or plain Yogurt for serving
Minced parsley for serving
Salt and pepper to taste
Heat the oil in a large heavy bottom pot over medium high heat. Add the leeks and onion and cook, stirring occasionally for about 8 minutes. Add the garlic, celeriac, potato and salt. Stir well. Add the stock and bring to a boil. Reduce the heat to medium-low and simmer until the vegetables are tender, about 25 minutes.
Remove from the heat and let the soup cool for a few minutes before transferring the soup (you may need to do this in batches) to a high speed blender and pureeing until completely smooth and creamy. (You can use a stick blender here but the soup wont be nearly as smooth and creamy.) Return the soup back to the pot, stir in the lemon juice and taste for seasonings. If the soup seems too thick add more stock or water. Keep the soup on low heat until ready to serve.
Serve with a drizzle of Crème Fraîche, or plain yogurt.