In a food processor, pulse 1/2 cup of the walnuts until finely ground; set aside. Add the dates to the processor and pulse until pureed; transfer to a medium bowl. Mix in remaining 1 cup walnuts and cardamom, if using.
Roll the date mixture into 1-inch balls (about 2 tsp. each). Roll half in the ground walnuts to coat and the other half in the coconut.