How to Make It
In a large frying pan, heat 2 tablespoons of the oil over moderate heat. Add the mushrooms, 1/2 teaspoon of the pepper, and the salt and cook, stirring occasionally, until the mushrooms are browned, 5 to 10 minutes.
Add the garlic and cook, stirring, for 30 seconds. Add the broth and bring to a simmer. Cook until reduced to about 1 cup, 2 to 3 minutes.
Meanwhile, in a large pot of boiling, salted water, cook the spaghetti until just done, about 12 minutes. Drain. Toss the spaghetti with the mushroom sauce, the remaining 2 tablespoons oil and 1/4 teaspoon pepper, and the Parmesan. Serve with more cheese.
Variation Add a couple of tablespoons chopped fresh herbs, such as chives, tarragon, thyme, or parsley, to the spaghetti along with the Parmesan.