Combine the basil, pine nuts, olive oil and garlic in a food processor until finely chopped. Transfer to a bowl and mix in the cheeses and black pepper. (This sauce does not call for salt because of the saltiness of the cheeses used.)
In a large pot, bring 5 quarts of water to a boil. Add about 1 tablespoon of salt. Add the pasta and stir frequently until al dente (about one or two minutes less than the cooking time recommended on the package). Drain the pasta, reserving 3 ounces of the cooking water.
Place the pasta, pesto sauce, water, and butter in a large bowl and toss until all ingredients are well mixed.Serve immediately.