Toast the Pistachios:

• In a small skillet over medium heat, melt 1 tbsp butter.
• Add chopped pistachios and toast for 1 minute until fragrant. Set aside.

Cook the Sausage:

• Heat a large Dutch oven over medium heat and coat the bottom with olive oil.
• Add the sausage, breaking it into pieces, and cook for 5-6 minutes until browned.
• Transfer to a plate and set aside.

Caramelize the Fennel & Onions:

• In the same pot, add red onion, fennel, and a pinch of salt.
• Cook for about 10 minutes, stirring occasionally, until caramelized and tender.

Cook the Pasta:

• Meanwhile, bring a large pot of salted water to a boil.
• Cook paccheri 2 minutes less than the package instructions, stirring occasionally.

Make the Sauce:

• Stir garlic and red pepper flakes into the caramelized fennel mixture, cooking for 30 seconds.
• Pour in white wine and reserved pasta water. Bring to a simmer and reduce for 3-4 minutes.

Combine Everything:

• Drain the pasta and add it to the pot, stirring well to coat.
• Stir in spinach, sausage, and remaining 2 tbsp butter until warmed through.
• Gradually fold in pecorino cheese until melted into the sauce.
• Add basil and parsley, stirring to combine.

Serve:

• Transfer pasta to a serving bowl and garnish with toasted pistachios, extra pecorino, and fresh herbs.