How to Make It
Preheat the oven to 500°. In a pot of boiling salted water, cook the pasta until al dente. Drain, reserving 1/4 cup of the pasta water. Transfer the pasta to a large bowl, cover with foil and keep warm.
Meanwhile, on a rimmed baking sheet, toss the mushrooms with 1/4 cup of the oil. Season with salt and pepper and spread the mushrooms in a single layer.
On another rimmed baking sheet, toss the onions with the remaining 2 tablespoons of oil; season with salt and pepper and spread in a single layer. Roast the mushrooms on the top rack and the onions in the middle of the oven for about 15 minutes, stirring after 10, or until the mushrooms are just tender.
Sprinkle the cheese over the mushrooms and the pine nuts over the onions and roast for 2 to 3 minutes, or until the cheese is melted and the pine nuts are toasted. Add the mushrooms and onions to the pasta along with the chives and toss well. If the pasta is dry, add a little of the reserved cooking water. Season with salt and pepper and serve.