Prepare a large bowl of ice water. Bring a large pot of water to a boil. Put the basil in a sieve and submerge in the boiling water, stirring, until bright green, 10 to 15 seconds. Submerge in the prepared ice water; drain on a kitchen towel and squeeze dry. Salt the boiling water and add the spaghetti; cook until al dente. Drain, reserving 1 cup of the pasta cooking water; return the pasta to the pot.
Meanwhile, using a food processor, puree the basil leaves, garlic, olive oil, nuts, parmesan, ricotta and 1/2 teaspoon salt. Add the pesto to the spaghetti and toss well. Top with extra basil leaves and serve with more parmesan.