Combine tahini, lemon juice, garlic and salt in a small bowl and mix until smooth. Mix in yogurt and cilantro and stir well to combine (see Tip). Add more lemon juice, if desired. Transfer to a bowl to serve.
Notes
Tip: If the tahini is very thick, you can use a food processor to help blend the dip. Place all ingredients except cilantro in the food processor and process until smooth. Add cilantro and pulse until well mixed, about 20 seconds.