Bring a large pot of salted water to a strong boil.
Add the pasta, stirring to avoid the pasta sticking together. Boil on high until just al dente.
Before draining, carefully remove two cups of pasta water. Set aside.
Drain the pasta, then add back to the pot it was cooked in over low heat.
Prepare the Tahini Pasta Sauce
While the pasta is cooking, whisk together the tahini, lemon juice, garlic, salt, and pepper in a medium bowl.
The tahini will seize up with the addition of the lemon juice and appear grainy, but continue to whisk until all the ingredients are well incorporated.
Carefully add ¼ cup of the pasta water to the sauce and whisk again until smooth.
Add the tahini pasta sauce to the cooked pasta in the pot, stirring to combine.
Add ½ cup pasta water along with the nutritional yeast, stirring until well incorporated. If necessary, add additional pasta water until the sauce evenly coats all the pasta. Discard any remaining pasta water.
Taste and add additional salt if desired. Sprinkle with parsley and chili flakes, if using, and serve immediately.
Notes
For Serving: red pepper flakes, fresh chopped parsley.
Salt the pasta cooking water generously!. This recipe relies on the pasta water to flavor both the noodles AND the finished sauce, so under-salted water produces a bland final dish. I add 1 to 2 tablespoons of kosher salt to a large pot of boiling water, which sounds like a lot but most of it gets discarded with the drained pasta.