Cook the spaghetti in salted water until al dente; reserve ½ cup pasta water and drain.
While the pasta cooks, heat the olive oil in a skillet over medium heat.
Sauté the onion and garlic for 3–4 minutes, until soft but not browned.
Add the spinach and cook until just wilted, about 1 minute.
In a blender or food processor, combine the spinach mixture with the basil, evaporated milk, queso fresco (or feta), Parmesan, and walnuts. Blend until smooth.
Pour the sauce into a skillet over medium heat. Add the cooked pasta and a splash of the reserved pasta water to loosen.
Toss until glossy and coated. Season with salt and pepper to taste.
Serve immediately, optionally topped with more cheese or a fried egg.
Enjoy!
Video
Notes
Storage and Reheating Store any pasta leftovers in the refrigerator for up to 3 days. If possible, keep the sauce and spaghetti separated to preserve the former’s color and texture. You can freeze the sauce for up to 3 months. I don’t recommend freezing the noodles as they get mushy. Reheat the sauce on the stove over low heat. To restore creaminess, add a splash of milk or vegetable broth.