Combine basil leaves, oil, nuts, garlic and salt in processor and process until creamy. Remove mixture and stir in cheeses.
Meanwhile cook pasta in plenty of boiling salted water until al dente. Drain, reserving a little of the water. Combine pesto sauce with 30 ml (2 tablespoons) hot water and stir in the butter.
Add stoned black olives to the pasta, then toss with the pesto sauce and serve.