Add walnuts to food processor and blend until finely ground. Add in the remaining ingredients and blend until a dough forms, about a minute.Turn out the dough onto a piece of parchment paper. Using your hands, roll pieces of the dough into small balls, about 1 inch around, and space out on parchment paper. After all of the balls are formed, press down on each ball to form a flat cookie. Place in the freezer for at least 30 minutes before serving. Store in an airtight container in the freezer.