Prepare the ingredients Bring approximately 3 quarts water to a boil in the pasta pot. Stir the tahini jar thoroughly, then measure 2 tablespoons into a small bowl. Finely grate the garlic and measure the lemon juice; wash the lemon first if using its zest.

Cook peas and pasta separately Prepare the frozen peas according to their package, including any required standing time, and drain excess liquid. Meanwhile, add 1 teaspoon salt and the farfalle to the boiling pasta water. Cook to al dente according to the pasta package, checking the thick center.

Save the cooking water Near the end of the pasta cooking, scoop out 1 cup water with a heatproof cup. Let its active bubbling stop before mixing it into the sauce. Drain the ready farfalle without rinsing.

Loosen the tahini in a bowl Whisk the lemon juice, garlic, and black pepper into the measured tahini. Gradually whisk in 3 tablespoons warm pasta water. If the mixture tightens or remains thick, continue whisking and add more water 1 tablespoon at a time until it pours from the spoon in a smooth ribbon.

Dress off the heat Return the drained pasta and fully cooked peas to the empty warm pasta pot, with the burner off. Pour over the loosened tahini mixture and fold immediately. Add more reserved water 1 tablespoon at a time until the bow ties are lightly coated and separate easily.

Finish and portion Fold in optional dill. Taste the mixed pasta before adding salt or more lemon. Divide between two bowls, add optional zest, and serve promptly. Keep the remaining water nearby for a final small adjustment if the sauce tightens before serving.