Start the water: Fill a large pot halfway with water and bring it to a boil over high heat.

Set a colander in the sink and put the spinach in the colander so it is ready when the pasta is drained.

Mix the sauce: In a large bowl, whisk together the tahini, lemon zest, lemon juice, olive oil, garlic, red pepper flakes, 1/2 cup of the Parmesan, and 2 tablespoons of the parsley. The mixture will look very thick at this point.

When the water boils, add enough salt so the water tastes lightly salty.

Add the spaghetti to the boiling water in the pot.

Stir the spaghetti for the first 30 seconds so the strands do not stick together.

Cook the spaghetti until it is tender with a little firmness in the center, using the package time as a guide.

Scoop out 1 1/2 cups of the pasta water into a measuring cup before you drain the spaghetti.

Whisk 1/2 cup of the hot pasta water into the tahini bowl until the sauce is smooth and loose enough to pour. If it still looks tight or grainy, whisk in a little more water.

Drain and wilt the spinach: Drain the spaghetti through the colander over the spinach. The heat from the pasta will wilt the spinach.

Return the spaghetti and spinach to the empty pot and set the pot over low heat.

Finish the pasta: Pour the tahini sauce into the pot.