In a food processor or coffee grinder, grind the pistachio to a fine powder, reserve a few whole ones for garnish.
In a medium saucepan, combine the milk and sugar. Cook over medium heat, stirring until the sugar is dissolved, and bubbles form around the edges of the pan. Remove from heat, add the pistachios, cool, cover and refrigerate overnight.
Strain the milk mixture through a fine-mesh sieve, pressing on the nuts with the back of a large spoon to get as much liquid from the nuts as possible. Transfer to an icecream maker and freeze according to the manufacturerOs instructions.