Preparation Combine dried porcini mushrooms and 1 cup boiling water in small bowl; let stand until porcini soften, about 30 minutes. Strain, reserving soaking liquid; coarsely chop porcini. Melt 4 tablespoons butter in large nonstick skillet over medium-high heat. Add shallots and sauté until slightly softened, about 2 minutes. Add fresh mushrooms and porcini and sauté until juices form, about 10 minutes. Add porcini soaking liquid, leaving any sediment behind. Stir until mushrooms are tender and juices evaporate, about 2 minutes. Season mushrooms to taste with salt and pepper. Transfer mushrooms to bowl. Cook green beans in large pot of boiling salted water until crisp-tender, about 5 minutes. Drain. Cool green beans under cold water; drain well. (Mushrooms and green beans can be prepared 1 day ahead. Cover mushrooms and refrigerate. Wrap green beans in paper towels, enclose in resealable plastic bag, then refrigerate.) Melt remaining 2 tablespoons butter in large nonstick skillet over medium heat. Add green beans and mushrooms. Cook until vegetables are heated through, stirring often, about 7 minutes. Season generously with salt and pepper. Transfer vegetables to bowl and serve.
Preparation Combine dried porcini mushrooms and 1 cup boiling water in small bowl; let stand until porcini soften, about 30 minutes. Strain, reserving soaking liquid; coarsely chop porcini. Melt 4 tablespoons butter in large nonstick skillet over medium-high heat. Add shallots and sauté until slightly softened, about 2 minutes. Add fresh mushrooms and porcini and sauté until juices form, about 10 minutes. Add porcini soaking liquid, leaving any sediment behind. Stir until mushrooms are tender and juices evaporate, about 2 minutes. Season mushrooms to taste with salt and pepper. Transfer mushrooms to bowl. Cook green beans in large pot of boiling salted water until crisp-tender, about 5 minutes. Drain. Cool green beans under cold water; drain well. (Mushrooms and green beans can be prepared 1 day ahead. Cover mushrooms and refrigerate. Wrap green beans in paper towels, enclose in resealable plastic bag, then refrigerate.) Melt remaining 2 tablespoons butter in large nonstick skillet over medium heat. Add green beans and mushrooms. Cook until vegetables are heated through, stirring often, about 7 minutes. Season generously with salt and pepper. Transfer vegetables to bowl and serve.