Whisk tahini, garlic paste, lemon juice, olive oil and the salt in a bowl until combined — the mixture will thicken, don’t worry about this.Add the water, a tablespoon at a time and whisking well after each addition until desired consistency. If making a spread, look for the consistency of peanut butter. If making a sauce, add enough water until the consistency of runny yogurt. Stir in the optional cumin, cayenne pepper and parsley. Taste for seasoning and adjust with additional salt or lemon juice.Store covered in the refrigerator up to 5 days.