The Sauce: Think of the porcini soaking liquid as a flavorful broth to use as the foundation for a rich, meaty-tasting sauce. A little sherry adds complexity. Finish with a touch of heavy cream and some of the starchy pasta water.
The Extras: If you have access to wild mushrooms, toss them in. Otherwise, look for an exotic blend and combine with crumbled Parmigiano-Reggiano and sage. A final splash of truffle oil takes this over the top.