How to Make It
In a large frying pan, melt the butter with the oil over moderate heat. Add the mushrooms and salt and cook, stirring occasionally, until the mushrooms are tender and well browned, about 8 minutes. Add the chicken broth and Boursin cheese and bring to a simmer while stirring.
Snap the tough ends off the asparagus and discard them. Cut the spears into 1/2-inch pieces. In a large pot of boiling, salted water, cook the pasta until almost done, about 6 minutes. Add the asparagus and cook until it and the pasta are just done, about 4 minutes longer. Drain. Toss with the mushrooms and sauce.
Many stores carry packages of already stemmed and sliced portobello mushrooms, a real convenience. You can use ten ounces of the presliced portobello caps in place of the one pound of whole mushrooms we call for here.