In a food processor, blend the chickpeas by themselves for 1 minute until powdery clumps form. Scrape down the sides and blend again until everything is the same consistency. Add the tahini, lemon juice, garlic and salt and blend until smooth. With the machine running, drizzle in 1 tablespoon of water at a time, until you get very smooth, light and creamy mixture. Taste and adjust seasonings, adding more salt, garlic or lemon if needed.