Bring a large pot of water to a boil over high heat. Meanwhile, fill the sink with water. Wearing rubber gloves, pull nettle leaves from stems into sink. Swish to rinse; drain. Add nettles to boiling water. Simmer until soft, 3 minutes. Drain, rinse with cool water, and squeeze out water. Whirl in a food processor until smooth.
Cook pasta as package directs. Meanwhile, melt butter over medium heat in pot used for nettles. Whisk in nettle purée, salt, and 1 cup hot pasta water; keep warm over low heat.
Drain pasta, reserving about 2 cups water. Add pasta to pot of sauce and toss with 3/4 cup parmesan, half of pine nuts, and some reserved water if needed so it's loose-textured. Transfer to a shallow bowl and sprinkle with remaining pine nuts and a little more parmesan if you like.
*Find nettles at farmers' markets. (They grow wild in many areas too.)
Note: Nutritional analysis is per serving.