This satisfying stew takes its intense flavor from fresh mushrooms and dried porcinis. To boost its nutritional value, you can add 10 ounces of baby spinach during the last few minutes of cooking. Paired with a loaf of hot, crusty bread and a simple salad, the ragout is hearty enough to serve as a meal on a cold winter night. Note that the dried beans require overnight soaking. The beans can be cooked a day ahead of serving; reheat before adding the mushroom mixture.
Place the beans in a medium-size bowl and add enough cold water to cover by 2 inches. Cover the bowl with plastic wrap. Let the beans soak overnight in the refrigerator.
Place the dried porcinis in a small bowl and add 2 cups of boiling water. Soak until the mushrooms are soft, 2 to 4 hours. Drain the mushrooms, reserving the soaking liquid (it has lots of flavor). Chop the mushrooms and set aside.
Heat half of the oil (3 tablespoons) in a large, heavy saucepan or Dutch oven over medium-low heat. Add the leeks, onion, and carrots, and season with salt and pepper. Cover and cook, stirring occasionally, until the vegetables are tender, about 15 minutes. Add 3 cups of the stock, the wine, tomatoes, bay leaves, thyme, sage, reserved chopped porcinis, and the reserved mushroom soaking liquid. (If there's sediment in the soaking liquid, be sure to leave that behind.)
Drain the beans and add them to the saucepan. Bring the mixture to the start of a simmer, then reduce the heat and simmer, uncovered, until the beans are tender, 1 1/2 to 3 hours, depending on the age of the beans. Stir the mixture occasionally, and add more stock by half-cupfuls so that the beans stay just covered with liquid while they cook.
Heat the remaining 3 tablespoons of oil in a large skillet over medium-high heat. Add the sliced mushrooms and shallots; cook, stirring frequently, until the mushrooms are begin to exude liquid, about 4 minutes. Add the garlic and continue cooking until the mushrooms are tender, 3 to 7 minutes more, depending on the variety. Season with salt and pepper to taste.
To serve, add the mushroom mixture to the hot bean ragout and cook over medium heat to warm the mushrooms. Sprinkle with parsley and serve hot.