Bring a large pot of salted water to boil and cook fettuccine according to package directions until al dente. Reserve 1/4 cup pasta cooking water before draining.

Heat olive oil and butter in a large skillet over medium heat until butter melts and begins to foam.

Add minced garlic and red pepper flakes, sautéing for 1-2 minutes until fragrant but not browned.

Add spinach and toss until just wilted, about 2-3 minutes. Season with salt and pepper.

In a bowl, whisk together ricotta cheese, lemon zest, lemon juice, and half of the Parmesan until smooth.

Add drained pasta to the skillet with spinach, tossing to combine evenly.

Remove from heat and add ricotta mixture, tossing quickly to create creamy sauce coating the pasta.

If sauce seems thick, gradually add reserved pasta water until desired consistency is reached.

Taste and adjust seasonings with salt, pepper, or lemon juice as needed.

Serve immediately topped with remaining Parmesan, fresh parsley, and black pepper.