Whisk lemon and garlic: Transfer the lemon juice to a medium bowl. Press the garlic into the bowl using a garlic press, or mince and add. Whisk to combine.
Add cumin, and salt. Whisk to combine.
Add the tahini and whisk the mixture until fully incorporated.
Add water: Add 2 tablespoons ice water at a time and whisk until smooth. The mixture may seize but it will eventually become creamy and smooth. Use up to 6 to 8 tablespoons water, or the amount needed for the desired texture.
Notes
For doubling the recipe, I recommend using a food processor or blender instead. Add all the ingredients (minus the water) to the canister of a food processor or blender and pulse until fully incorporated. Then gradually add the water through the drizzle basin or feed tube until the desired consistency. You can also easily add fresh herbs using this method for a blended herby falafel sauce.
The mixture may seize when whisking, but don't panic. It will eventually become creamy and smooth as you keep whisking and adding water as needed.
Storage: Refrigerate any remaining sauce in an airtight container for up to 7 days.