Preparation Preheat oven to 400°F. Line 2 large baking sheets with foil. Divide mushrooms between prepared baking sheets. Drizzle mushrooms on each sheet with 3 tablespoons oil. Sprinkle generously with salt and pepper; toss to coat. Cover with foil. Bake mushrooms 30 minutes. Uncover and continue baking until mushrooms are tender and still moist, about 15 minutes longer. Cool slightly. Puree half of mushrooms with 1 can broth in blender until smooth. Set mushroom puree aside. Melt butter in heavy large pot over medium-high heat. Add onion and garlic and sauté until onion is tender, about 8 minutes. Add Madeira and simmer until almost all of liquid evaporates, about 2 minutes. Add flour; stir 2 minutes. Add 2 cans broth, cream, and thyme. Stir in remaining cooked mushroom pieces and mushroom puree. Simmer over medium heat until slightly thickened, about 10 minutes. Season soup to taste with salt and pepper. (Can be made 1 day ahead. Cool slightly, then cover and refrigerate. Bring to simmer before serving, thinning with additional broth if necessary.)
Preparation Preheat oven to 400°F. Line 2 large baking sheets with foil. Divide mushrooms between prepared baking sheets. Drizzle mushrooms on each sheet with 3 tablespoons oil. Sprinkle generously with salt and pepper; toss to coat. Cover with foil. Bake mushrooms 30 minutes. Uncover and continue baking until mushrooms are tender and still moist, about 15 minutes longer. Cool slightly. Puree half of mushrooms with 1 can broth in blender until smooth. Set mushroom puree aside. Melt butter in heavy large pot over medium-high heat. Add onion and garlic and sauté until onion is tender, about 8 minutes. Add Madeira and simmer until almost all of liquid evaporates, about 2 minutes. Add flour; stir 2 minutes. Add 2 cans broth, cream, and thyme. Stir in remaining cooked mushroom pieces and mushroom puree. Simmer over medium heat until slightly thickened, about 10 minutes. Season soup to taste with salt and pepper. (Can be made 1 day ahead. Cool slightly, then cover and refrigerate. Bring to simmer before serving, thinning with additional broth if necessary.)