Instructions: Place basil, garlic, and walnuts in a food processor and process 15 seconds.

With machine on, pour oil through feed tube in a steady stream until almost 1 cup of oil has been used. With machine still running, add Parmesan and pecorino (or Romano) cheese, and then the remaining oil. Taste and season pesto sauce with salt, if needed.

Cook fettuccine in a large pot of boiling salted water until tender but still firm, 2 to 4 minutes, drain. Pour pasta into a warmed large bowl and toss with butter, then with 1 cup of the pesto sauce. Pass remaining pesto on the side.

Freese any remaining sauce for future use.

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