Grated Parmesan, for serving
Preparation:
1. Bring a large pot of salted water to a boil. Add pasta and cook according to package instructions until al dente.
2. After pasta has been cooking for about 2 minutes, melt the butter in a large skillet over medium-high heat. Add the pistachios, garlic and capers and cook, stirring to keep the garlic from scorching, until fragrant, about 1 minute.
3. Add spinach to skillet one handful at a time, season with salt and cook, tossing, until wilted, about 1 or 2 minutes.
4. Using a slotted spoon, transfer pasta to the skillet along with 1/2 cup pasta water. Season with salt and pepper and cook over medium-high, tossing, until liquid reduces and coats the pasta, 2 to 3 minutes; season with salt and pepper. Serve topped with Parmesan.