Mince the garlic cloves finely and measure out the nutritional yeast, salt, lemon juice, lemon zest, and vegetable broth. If your cashews aren't already soaked, place them in a bowl of hot water and let them sit for 15-20 minutes to soften—this will ensure your sauce becomes silky and smooth when blended.

Bring a large pot of salted water to a boil and add the spaghetti. Cook according to package directions until al dente, then drain well in a colander. Set the cooked pasta aside—I like to lightly toss it with a tiny bit of olive oil to prevent sticking while you prepare the sauce.

Heat the olive oil in a large skillet over medium heat. Add the minced garlic and cook for about 1 minute, stirring constantly, until fragrant—don't let it brown or it will taste bitter. Add all the spinach to the skillet and stir frequently for 2-3 minutes until completely wilted and any excess moisture has mostly evaporated.

Transfer the wilted spinach and garlic from the skillet to a blender. Add the drained soaked cashews, nutritional yeast, salt, lemon juice, lemon zest, ground nutmeg, and vegetable broth. Blend on high speed for 1-2 minutes until completely smooth and creamy, scraping down the sides as needed. Taste and adjust seasoning with extra salt or lemon juice if desired.

Pour the blended sauce back into the skillet over low heat and gently warm it through for 1-2 minutes, stirring occasionally. Add the cooked pasta from Step 2 to the skillet and toss everything together until the pasta is evenly coated with the creamy green sauce. Divide into bowls and serve immediately with your choice of toppings.