Remember the green bean casserole made with nothing but convenience ingredients: frozen or canned green beans, canned cream of mushroom soup and, for the topping, canned fried onions? Here it is again, only fresher and better.
Makes 6 servings.
Melt 2 tablespoons butter in heavy large skillet over medium-high heat. Add all mushrooms and thyme; sauté 5 minutes. Add 2 tablespoons shallots; sauté until mushrooms are tender, about 3 minutes. Add Madeira and simmer until almost all liquid evaporates, about 2 minutes. Add cream and simmer until slightly thickened, about 2 minutes. Set sauce aside.
Cook beans in large pot of boiling salted water until just tender, 5 minutes. Drain. Transfer to bowl of ice water; cool. Drain. (Sauce and beans can be made 6 hours ahead. Cover separately; chill.)
Pour enough oil into large deep saucepan to reach depth of 4 inches. Heat oil to 350°F. Place 1/4 of leeks in small metal strainer. Lower strainer into oil; fry until golden, 40 seconds. Lift strainer from oil. Drain leeks on paper towels. Repeat with remaining leeks in 3 more batches. Season leeks with salt.
Melt 1 tablespoon butter in heavy large skillet over medium heat. Add beans and remaining 1 tablespoon shallots; toss to heat through. Season with salt and pepper. Place beans on platter.
Bring sauce to simmer. Spoon sauce over beans. Sprinkle with fried leeks.