Place the dried mushrooms in a small pot with the stock. Bring to a simmer and reduce the heat to reconstitute the dried mushrooms.
Bring a large pot of water to a boil for the pasta and pre-heat a Dutch oven or large saucepot over medium-high heat with four turns of the pan of olive oil. Add the pancetta and stir to render, 2 minutes. Add the fresh mushrooms and brown. Once browned, season with salt and pepper. Add the garlic, onions and sage and stir for a few minutes to soften. Add the wine and stir until mostly evaporated. Add the tomatoes to the mushrooms and stir. Remove the porcini mushrooms from their stock and chop; add to the sauce. Add all but the last few spoonfuls of stock. Any grit from dried mushrooms will have settled here.
Salt boiling water and cook the pasta to al dente. Add half a cup of the starchy cooking water to the pasta sauce and drain the pasta. Toss the pasta with the sauce and top with Pecorino cheese and parsley before serving.