1 lb walnuts in the shell
2 garlic cloves, minced
2 to 3 T extra-virgin olive oil as needed
1/4 cup minced flat-leaf parsley
salt to taste
1 lb spaghettini, spaghetti, linguine, or other long pasta
6 quarts water
1/4 cup ricotta cheese
freshly ground black pepper to taste
1/2 cup freshly grated Parmigiano cheese
Shell the walnuts and pound to a paste in a mortar or in a food processor. If you're using a food processor, add a tablespoon of water; otherwise the walnuts might become over processed and exude their oil.
In a saucepan over medium-low heat, gently sauté the garlic in a tablespoon of olive oil until the garlic is soft but not brown-about 10 minutes.
Add the walnuts and parsley with a pinch of salt. Stir to combine the ingredients well and cook for about 5 minutes, adding another tablespoon or more of oil if it seems necessary to keep the walnuts from burning.
Cook the pasta in lightly salted water.
While the pasta is boiling, add 2 tablespoons of the pasta water to the walnut sauce and continue cooking the sauce over very low heat.
Blend the ricotta into the sauce, using a fork to mix it well.
Taste and add salt if necessary and lots of freshly ground pepper.
As soon as the pasta is done, drain it, turn it into a heated bowl, and immediately turn the sauce over the pasta and mix well, adding about half the grated Parmigiano. Serve immediately, passing the rest of the cheese at the table.