Soak the cashews in water for a minimum of 4 hours. Drain and rinse well before using.
In a large pot, bring 4 to 6 quarts of water to a rolling boil.
Meanwhile, in a high-speed blender, combine the cashews, water, lemon juice, vinegar, yeast, garlic, 2 teaspoons of the salt, and the pepper. Blend until smooth.
With the blender running on low speed, slowly add the olive oil until smooth.
Add the remaining 2 tablespoons of salt to the boiling water.
Add the bucatini and cook until very al dente, a little more than half the recommended cooking time.
Pour all the cacio e pepe sauce into a large sauté pan and warm it over low heat for 3 to 4 minutes, just enough to make it piping hot.
Use pasta tongs to transfer the bucatini to the sauté pan and add ½ cup of the pasta cooking water.
Cook the bucatini in the sauce, tossing it around until it absorbs all the water and is perfectly al dente. Check to make sure the pasta does not overcook. Add more pasta water if needed.
Top with parsley and pepper.