Leek soup with fried potatoes and herbs

Heat butter in a heavy pot over medium heat. Add leeks, onion, and garlic, and season with salt. Sauté, stirring often, until soft, about 5-7 minutes. Add 1 cup of water and simmer, stirring occasionally, for 25-30 minutes (vegetables will become very soft). Let cool slightly, then transfer half of the mixture to a blender, adding half of the milk, cream, and yogurt. Blend until smooth, then pour into a large bowl. Repeat with the second half of the mixture, adding the second half of the milk, cream, and yogurt.

Pour the soup into a pot and heat over medium heat, adding water by ¼ cup until the mixture is thick enough to hold potatoes on its surface while remaining liquid enough that a spoon doesn't leave a mark. Season with salt and pepper to taste. It can be made in advance: the soup can be prepared up to 2 days before serving. Cover and refrigerate.

Wash the potatoes with cold water, let them drain, and dry completely with paper towels. Pour oil (5 cm deep) into a deep fryer with a thermometer. Heat over medium heat to 180˚C. Fry the potatoes until golden brown for about 2 minutes, adding them in batches and reheating the oil to 180˚C between batches. Use a slotted spoon to transfer the potatoes to a paper towel to remove excess oil. Fry the parsley and rosemary in the oil until translucent for about 15 seconds. Add the potatoes and let cool; season with salt. Serve the soup garnished with potatoes and herbs.