The illusion of cream in this silky soup comes from thoroughly pureeing it in a blender. Do use the Rich Chicken Stock; it makes all the difference. Slideshow: Warming Soup Recipes
Preheat the oven to 450°. In a large bowl, toss the oyster mushrooms with the 2 tablespoons melted butter and season with salt and pepper. Arrange the mushrooms on a large rimmed baking sheet in a single layer and bake for about 20 minutes, or until they have begun to brown and crisp. Remove any crisp mushrooms to a plate; continue baking the rest for 10 minutes, or until crisp.
Meanwhile, in a large nonreactive saucepan, melt the 3 tablespoons butter over moderate heat. When the foam subsides, add the shallots and reduce the heat to low. Cook, stirring a few times, until softened, about 5 minutes. Increase the heat to moderately high and add the cremini mushrooms. Season with salt and pepper and cook, stirring, until wilted, about 4 minutes. Add the wine and boil until reduced by half, about 3 minutes. Stir in the flour until well blended. Gradually whisk in the Rich Chicken Stock and bring to a simmer. Reduce the heat to low, cover and cook until the mushrooms are very tender, about 15 minutes.
Working in batches, puree the soup in a blender until completely smooth. Reheat the soup. Season with the lemon juice and salt and pepper. Ladle into rimmed soup plates and garnish with the chips and chives.
The soup and mushroom chips can be refrigerated for up to 1 day. Recrisp the chips in a 400° oven.
If you can't find oyster mushrooms, use thinly sliced cremini or white mushrooms for the chips instead.