1 1/2 pounds large Yukon Gold potatoes, peeled and very thinly sliced
1 tablespoon chopped thyme leaves
Pinch of cinnamon
Salt and freshly ground pepper
3 tablespoons cream sherry
1 teaspoon fresh lemon juice
In a large soup pot, heat the olive oil until shimmering. Add the onions and garlic, cover and cook over moderate heat, stirring occasionally, until softened, about 5 minutes. Add the stock, chestnuts, potatoes, thyme and cinnamon; season with salt and pepper. Cover and cook over moderate heat until the potatoes are very tender and broken up, about 15 minutes.
In a blender, puree the soup. Return the soup to the pot and stir in the sherry and lemon juice. Ladle into shallow bowls and serve.