Place all the ingredients (except the extra 1/4 C pistachios) into a food processor. Blend for 1 minute or until the mixture becomes smooth and thick like a paste. Scoop out enough of the mixture to form a 1 inch ball (about 1 1/2 tbsp) and roll between your hands to create a small, round ball.
Set aside and repeat until all the mixture has been rolled into balls. Place the chopped pistachios on a plate and roll the balls through the nuts, pressing them into the balls so they stick. Refrigerate for 15 minutes.