The secret to achieving the creamy, fluffy texture known in Israel is the gradual addition of ice-cold water to the Tahini paste. When Tahini paste first encounters lemon juice and water, it will thicken (or 'seize'), lighten in color, and appear curdled – this is correct! Continue whisking and adding water until the mixture transforms into a smooth, light sauce.
In a medium bowl, combine the Tahini paste, lemon juice, minced garlic, salt, and ground cumin (if using).
Begin vigorously whisking the mixture with a whisk or fork. The Tahini will immediately thicken and change color from brown to a light creamy white – this emulsification process is correct and necessary.
Start gradually adding the ice-cold water, one tablespoon at a time. Whisk after each addition until the liquid is fully incorporated into the mixture.
The mixture will initially thin out, then thicken again, and then thin out again, becoming increasingly pale and fluffy. Use about 4 tablespoons of ice water in total, or more if you desire a thinner, pourable sauce.
Taste the Tahini sauce. If it's too thick, add more ice water (by teaspoons). If you want a more zesty flavor, add more lemon juice or salt.
The finished sauce should be creamy, smooth, and have the consistency of heavy cream or a slightly thinner yogurt.
Transfer the sauce to a serving bowl. Just before serving, drizzle it with a little extra virgin olive oil.
Garnish with chopped parsley or a sprinkle of ground paprika. Serve cold or at room temperature.