Bring a large pot of well-salted water to a boil. Set up a bowl of well-salted ice water. Cook the broccoli rabe in the boiling water for 1 to 2 minutes and then immediately plunge in the salted ice water. This will prevent the broccoli rabe from being overcooked and will set the lovely green color.
Drain the broccoli rabe and squeeze out any excess water; coarsely chop. Place the broccoli rabe in the bowl of a food processor and puree until it is a coarse paste. Add the pistachios and parmigiano and puree until smooth. Taste and adjust the seasoning; you probably will need more salt. Add the ricotta and pulse until combined. Taste for seasoning once again-it should be full-flavored, slightly bitter and creamy at the same time. Set aside.
Bring a large pot of well-salted water to a boil. (If you are making the pasta right after the pesto, just use the broccoli rabe blanching water.) Cook the pasta 1 minute less than the cooking time on the package.
While the pasta is cooking, place the pesto in a large skillet and add about 1 to 1 1/2 cups of the pasta cooking water; place over medium-high heat. When the pasta is ready, drain and add to the skillet with the pesto. Stir vigorously to combine and cook until the sauce is creamy and heated through, 1 to 2 minutes; add salt to taste. Remove from the heat, add 1 to 2 tablespoons olive oil, if desired, and stir vigorously. Garnish with more parmigiano. Voila!