In a food processor, combine the pistachios, reserved garbanzo bean liquid (but not the garbanzo beans), and olive oil. Blend on high for 1 minute until smooth.
Add the drained garbanzo beans, cumin, tahini, lemon juice, garlic cloves, and ice. Blend for 1–2 minutes, stopping occasionally to scrape down the sides, until the mixture is creamy. Adjust seasoning and tahini to taste.
Transfer the hummus to a serving dish and garnish with chopped parsley and a few crushed pistachios for added texture.
