Begin by soaking your raw cashews in water for 2-4 hours. This softens them, making them easier to blend into a creamy sauce.
In a large pot, bring salted water to a boil. Add the fettuccine and cook according to package instructions until al dente. Reserve about 1/2 cup of the pasta cooking water, then drain the pasta and set it aside.
In a blender or food processor, combine the soaked cashews, 2/3 cup of water, garlic cloves, lemon juice, lemon zest, crushed red pepper, sea salt, and cracked pepper. Blend until smooth and creamy, scraping down the sides as necessary. If the sauce is too thick, add a little more water until you reach your desired consistency.
In a large skillet over medium heat, add a splash of water or a drizzle of olive oil. Add the baby spinach and sauté until wilted, about 2-3 minutes.
Add the cooked fettuccine to the skillet with the sautéed spinach. Pour the lemon garlic cashew cream sauce over the pasta and toss to combine. If the sauce is too thick, add some of the reserved pasta water to thin it out as needed.
Divide the Lemon Garlic Cashew Cream Sauce with Fettuccini among plates. For an extra touch, garnish with additional lemon zest or a sprinkle of crushed red pepper. Serve immediately and enjoy the delightful flavors!