Cook the pasta according to the package directions. Dip a glass measuring cup or coffee mug into the water and reserve about 1½ cups. Drain the pasta, return it to the pot, and set aside while you make the sauce.
Blend the sun-dried tomatoes, cashews, 1 cup reserved pasta water, lemon juice, garlic, and salt and pepper in a high-speed blender until the sauce is very smooth. Add more reserved pasta water as needed if the sauce is too thick to blend.
Add the sauce to the cooked pasta and toss until well coated, adding a little extra reserved pasta water as needed.
Serve the pasta immediately topped with fresh basil or parsley, if desired.
Notes
Storing: Leftover pasta will last covered and refrigerated for up to 3 days. For best results, do not freeze.Sun-dried tomatoes: This recipe calls for the ones in a jar packed in olive oil. If you prefer an oil-free version, you can use the dry ones sold in bags and in bulk bins. But you will need to soak them in a bowl of water for at least 2 hours to reconstitute them.Raw cashews: Look for raw cashews rather than roasted cashews. Bags of halves and pieces are usually less expensive than whole raw cashews.