Bring a large pot of salted water to a boil. Add the pasta and cook until al dente according to package directions. Before draining, scoop out about 1/2 cup of pasta water and set aside.

While the pasta cooks, zest the lemons and squeeze out the juice. Measure out 1 cup ricotta and grate the Parmesan.

In a large skillet, warm the olive oil over medium heat. Add the minced garlic and red pepper flakes (if using). Sauté for about 30 seconds—until fragrant but not browned.

Add the fresh spinach to the skillet and sauté until wilted, about 2–3 minutes. If using frozen spinach, ensure it’s well-drained before adding.

Reduce heat to low. Stir in the ricotta, lemon zest, lemon juice, and Parmesan. Add 2–4 tablespoons of the reserved pasta water to loosen the mixture. The sauce should be creamy and glossy. If it seems too thick, add more pasta water, one tablespoon at a time.

Add the drained pasta directly to the skillet and toss to coat. If you want extra silkiness, stir in the butter now. Taste and season with salt and lots of black pepper.

Serve immediately with extra Parmesan, a drizzle of olive oil, and an extra sprinkle of lemon zest if you’re feeling fancy.