Place the cashews and water in a small bowl, and soak overnight. Drain and rinse cashews. Editor's Tip: Don't skip this step! The cashews need to be softened or the sauce will be gritty and grainy. If you're in a rush, place the cashews in a small saucepan and cover them with water. Bring the water to a boil, then remove the pan from the heat. Let the pan stand for 15 minutes before draining and rinsing the cashews.
Cook the linguine according to the package directions. Reserve 2 cups pasta water and drain the remaining water. Return the pasta to the pot.
Place the soaked cashews, reserved pasta water, onion, garlic, nutritional yeast, lemon juice, salt, pepper and rosemary in a blender. Editor's Tip: If you don't have any reserved pasta water, use 2 cups of your favorite unsweetened nondairy milk alternative. Puree until smooth. Editor's Tip: If the sauce looks too thick, add extra water or milk until it reaches the desired consistency. This is also a good time to taste the sauce and add more seasonings, if needed.
Add the sauce to the pasta in the pot, and toss to combine. Editor's Tip: The pasta's ambient heat should warm the sauce through. If needed, you can heat the sauce over gentle heat.
