In a large saucepot, over high heat melt
the butter and add the leeks
and garlic. Cook over medium heat until they are translucent. Add the hot stock and whisk to combine.
In a separate bowl, whisk
together the riced potatoes, buttermilk, sour cream, and grated Parmesan. Add this mixture to the soup
stirring constantly. Season with salt and pepper. Remove from the heat and add the Sherry vinegar.
Ladle into bowls and garnish