Bring a large pot of salted water to a boil. Cut the portabella caps in half. Slice each half crosswise into 1/4-inch slices.
Heat the olive oil and butter in a large sauté pan over medium-high heat. When the butter is bubbling and nutty brown, add the portabellas and season with salt and pepper. Sauté until they begin to lose their juices and are well browned, about 5 minutes. Add the garlic, shallots, and sage and cook until fragrant, about 2 minutes. Add the sherry and simmer over medium heat until the portabellas are tender and the liquid has reduced by about half, about 8 minutes.
Meanwhile, cook the linguine al dente.
Add the heavy cream to the pan with the mushrooms and stir; reduce until the sauce coats the back of a spoon. Drain the pasta and add it to the pan of portabellas. Add the cheese and parsley and toss to coat. Top with additional parsley, if you like.
nutrition information (per serving):
Photo: Scott Phillips