Food & Wine's Marcia Kiesel updates a Forties' favorite. Slideshow: More Cold Soups
In a saucepan, heat the oil over moderately high heat until shimmering. Add the shallots and cook over moderately low heat, stirring often, until golden, about 5 minutes. Transfer to paper towels.
Melt the butter in a large nonreactive saucepan. Add the leeks and onion and cook over moderately low heat, stirring, until softened but not browned, about 12 minutes. Add the wine and cook over moderately high heat until reduced by half, about 3 minutes. Add the stock, potatoes, bay leaves, salt and pepper. Bring to a boil, then simmer over low heat, partially covered, until the potatoes are tender, about 25 minutes.
Working in batches, puree the soup in a blender, then transfer to a bowl and let cool. Stir in the milk, cream, salt and pepper. Refrigerate until chilled, at least 4 hours or overnight. Season with salt and pepper and garnish with the chives and shallots.