In a large nonstick saucepan or Dutch oven, heat the oil. Saute the mushrooms and scallions until the mushroom liquid evaporates, about ten minutes. Stir in the broth, potatoes, wine, thyme, caraway seeds and salt; bring to a boil. Reduce the heat and simmer, partially covered, until the potatoes are tender, about twenty minutes. Transfer to a blender and remove the knob in the lid, puree. Return the soup to the saucepan; bring back through a boil. Remove from the heat and stir in the half-and-half. Serve immediately.