1. In a large pot, bring 2 quarts of water to a rapid boil. Pour in the edamame. Return to a boil and cook for about 6 minutes, or until the beans are creamy inside and easy to smash with a fork. Drain the edamame and dunk in a large bowl of cold water, about 3 minutes. Drain when cool.
2. In a food processor fitted with a metal blade or in a blender, combine the edamame, tahini, oil, lemon juice, garlic, and salt. Pulse, scraping down the sides of the bowl occasionally, until the mixture is pureed smooth. Add cold water, a little at a time, until the mixture is creamy.
Serve as a party dip or snack with toasted pita or seasonal vegetables such as cucumber, squash, or orange bell pepper.
Tahini is prepared ground sesame seeds. Look for it in the gourmet cheese section of the supermarket.