Combine dried mushrooms and boiling water in a bowl; cover and let stand 30 minutes or until tender. Drain mushrooms in a sieve lined with a paper towel over a bowl; reserve liquid. Rinse mushrooms; drain well. Chop.
Place fava beans in a large pot of boiling water; cook 40 seconds. Drain; rinse with cold water. Drain well. Remove tough outer skins from beans.
Heat a large skillet over medium-high heat. Add oil to pan, swirling to coat. Add onion to pan; sauté 3 minutes or until tender. Add fresh mushrooms and garlic; sauté 2 minutes. Add chopped rehydrated mushrooms, reserved liquid, fava beans, and marjoram. Cook until liquid is reduced to 1/2 cup (about 5 minutes).
Cook pasta in boiling water with 1 tablespoon salt according to package directions, omitting additional fat. Drain. Add pasta, mascarpone, and remaining ingredients to fava bean mixture; toss gently to coat.
Wine Suggestion: The wait for weather warm enough to crack open a bottle of rosé has always been a difficult one. By the time the birds start chirping, I'm up to my eyeballs in pink. Rosés come in styles that range from light and dry to full and fruity. And when they are from Spain, all the better. This morel and fava bean pasta dish begs for a full, tropical fruit-laden rosé from Bodegas Muga, Rioja Rosé, 2009 ($13). Its elegant, fresh citrus flavors cut the creamy mascarpone, while its laid-back herbal notes pair remarkably with the meaty morels. -Alexander Spacher