Next time you buy beets at the store or farmer's market, don't throw out the tops! A quick whirl in the food processor with toasted pistachios, smashed garlic, and olive oil makes a super easy (and frugal) pesto. Toss with penne for a tasty weeknight dinner.
Pistachios: Toast pistachios in a skillet over low heat until they're light brown in spots, with a toasty aroma, 2–3 minutes.
Greens: Pull leaves from stems and wash thoroughly (they can be sandy). Bring a large pot of salted water to a boil, and blanch the greens for 20 seconds (to preserve their color). Using a slotted spoon, transfer them to a bowl of ice water (to stop the cooking).
Pesto: Purée the pistachios, garlic, and oil in a food processor until nuts are combined with the oil but still chunky (you don't want to make nut butter). Remove greens from the ice water and squeeze out excess water. Roughly chop them and add to the food processor with a pinch of salt. Pulse to combine, leaving the pesto slightly chunky. Taste for seasoning. Push down the sides of the bowl and pulse 5 more seconds.
Assembly: Toss half of the pesto with the cooked penne, adding more as needed. Serve immediately.
Extra pesto can be put in a lidded jar, topped with a layer of parchment paper or olive oil, and kept in the fridge for up to 1 week.