Bring a medium sauce pot of generously salted water to a boil. Stir in the pappardelle and cook, stirring occasionally, until just tender, 3 to 5 minutes. Drain the pappardelle, reserving ½ cup [¾ cup] pasta cooking water. Return the pappardelle to the pot; drizzle with about 1 tablespoon oil and toss to keep the noodles from sticking.
While the water heats and the pappardelle cooks, prepare the remaining ingredients and start the sauce.

• Peel and thinly slice the shallots.
• Finely chop, press, or grate the garlic.
• Strip the rosemary leaves from the stems and coarsely chop enough to measure 1 teaspoon [2 tsp]. Save any remaining rosemary for another use.
• Cut the mushrooms into ¼-inch-thick slices.
• Zest the lemon; cut the lemon into wedges for garnish.

In a large frying pan over medium heat, warm 2 tablespoons oil until hot but not smoking. Stir in the shallots, garlic, rosemary, and mushrooms and cook until the shallots and mushrooms are starting to soften, 3 to 4 minutes. Add ¼ cup [⅓ cup] white wine (from your pantry) or water and cook, stirring occasionally, until the mushrooms are tender and the liquid has mostly evaporated, 3 to 4 minutes. Stir in the spinach, pappardelle, and ¼ cup [⅓ cup] reserved pasta cooking water. Cook over medium-high heat until the sauce has thickened and the spinach is just wilted, 1 to 2 minutes. Add more pasta cooking water if dry.
Remove from the heat, stir in the lemon zest, and season to taste with salt and pepper.

Transfer the pappardelle to individual bowls. Garnish with the walnuts and ricotta and serve with the lemon wedges.