Bring a large sauce pot of generously salted water to a boil.

• If using, let the butter come to room temperature.
• Peel and finely chop enough shallots to measure ½ cup.
• Finely chop, press, or grate enough garlic to measure 2 teaspoons.
• Zest the lemons.
• Juice the lemons.
• Strip the parsley leaves from the stems.
• Coarsely chop the parsley leaves.
• Coarsely chop the hazelnuts.

To the pot with the boiling water, add the pappardelle a few noodles at a time and cook, stirring occasionally, until just tender, 3 to 5 minutes. Drain the pappardelle, reserving ½ cup pasta cooking water. Return the pappardelle to the pot; drizzle with 1 tablespoon oil and toss to keep the noodles from sticking.
While the pappardelle cooks, prepare the vegetables and finish the pasta.

In a large frying pan over medium heat, warm 1 to 2 tablespoons oil until hot but not smoking. Add the shallots, garlic, and as many chile flakes as you like, season generously with salt, and cook, stirring occasionally, until fragrant, 2 to 3 minutes. Stir in the spinach and peas and cook until the spinach is just wilted, 1 to 2 minutes. Add the pappardelle, reserved pasta cooking water, lemon zest, and parsley.
Remove from the heat and stir in 2 tablespoons lemon juice, the butter, if using, or 2 tablespoons oil, and half the Parmesan (set aside the rest for serving). Season to taste with salt and pepper.

Transfer the pappardelle to individual bowls. Crumble the ricotta salata over the top, garnish with the hazelnuts, and serve with the remaining Parmesan.