Heat a large pot of water for the pasta. Boil the pasta to al dente. In the last minute of cooking, remove 1 cup of the cooking liquid for the pasta sauce and reserve. Add the asparagus tops to the pasta at the same time and cook for 1 minute. Drain the pasta and asparagus together.

Meanwhile, make the pesto. Combine the asparagus bottoms, scallion, garlic, and pistachios in the bowl of a food processor. Zest the lemon into the mixture. Add the olive oil, and pulse until finely chopped and a paste forms.

Cut the zested lemon into wedges for serving.

When the pasta is cooked, add it pack to the pot with the asparagus tops and pesto. Splash in ½ cup of the reserved pasta water and stir everything together. Taste, and add more pasta water if you'd like a saucier pasta or more salt if needed.

Serve with lemon wedges. Enjoy!