This satisfying stew takes its intense flavor from fresh mushrooms and dried porcinis. Paired with a loaf of hot, crusty bread and a simple salad, it's hearty enough to serve as a meal on a cold winter night.
Note that the dried beans require soaking overnight. 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, chopped porcinis and the reserved mushroom soaking liquid. (Leave behind any sediment in the soaking liquid.)
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. Stir the mixture occasionally, and add more stock by half-cupfuls so that the beans stay just covered with liquid as they cook.
Heat the remaining oil in a large skillet over medium-high heat. Add the sliced mushrooms and shallots, and cook, stirring frequently, until the mushrooms begin to give up their liquid, about 4 minutes. Add the spinach and garlic, and continue cooking until the mushrooms are tender, 3 to 7 minutes more. Season with salt and pepper to taste.
To serve, add the mushroom mixture to the hot beans. Sprinkle with parsley and serve hot.