Bring a large pot of water to a rolling boil. Add the fine sea salt, then cook the spaghetti or bucatini until just al dente according to the package directions.
Before draining, reserve at least 1 cup (240 milliliters) of the hot pasta water. Drain the pasta and set aside.
Make the sauce:
Soak cashews in boiling water for 20 minutes, then drain.
Blend the raw cashews with the hot water until completely smooth and creamy. The texture should resemble light cream rather than a thick paste. Set aside.
Place a large skillet over medium heat. Add the freshly cracked black pepper and toast it dry for about 30 seconds, just until fragrant.
Add the vegan butter and let it melt, swirling the pan so the pepper infuses into the butter.
Lower the heat to medium-low. Add 1/2 cup (120 milliliters) of the reserved pasta water to the skillet and whisk to create a glossy butter sauce. Whisk in the blended cashew cream.
Finish:
Add the drained pasta directly to the skillet and toss well to coat.
Sprinkle in the nutritional yeast and continue tossing. Remove the pan from the heat.
Add more reserved pasta water a few tablespoons at a time until the sauce lightly coats the pasta. You may not need all of it.
Taste and add the fine sea salt if needed. Serve immediately with extra black pepper on top and vegan Parmesan cheese, if using.
Notes
Refrigerator: Store leftover cacio e pepe in an airtight container for up to 3 days. I don’t recommend freezing this recipe, as the consistency of the sauce will change.
To reheat: Warm gently in a skillet or the microwave with a splash of water to loosen the sauce.