Rinse dried porcini thoroughly. Combine porcini and 2/3 cup boiling water in a bowl; cover and let stand 30 minutes. Drain in a sieve over a bowl, reserving 1/4 cup soaking liquid. Chop the porcini.
Cook pasta with 1 tablespoon salt in boiling water 10 minutes or until al dente; drain in a colander over a bowl, reserving 1/4 cup cooking liquid.
Heat oil in a large skillet over medium-high heat. Add the shallots, mushroom blend, and garlic; sauté 5 minutes, stirring frequently. Stir in the porcini, dry sherry, and remaining 1/4 teaspoon salt; cook 1 minute or until the liquid evaporates.
Finely grate 1 ounce cheese; crumble remaining cheese. Reduce the heat to medium. Stir in the pasta, the 1/4 cup reserved cooking liquid, the 1/4 cup reserved porcini soaking liquid, 1/4 cup grated cheese, the heavy cream, and black pepper into mushroom mixture; toss well to combine. Drizzle with a dash of olive oil; toss well. Serve pasta, sprinkle more freshly grated Parmigiano-Reggiano and garnish with chives.