Finely grind 1 cup of the pistachios and 1/2 cup of the sugar in a food processor, being careful not to turn the mixture into butter. Bring the milk and cream to a boil in heavy large saucepan. Remove from heat.
Combine the egg yolks and remaining 1/2-cup sugar in a mixing bowl and whisk to blend. Gradually whisk 1 cup of the hot milk mixture into the eggs. Gradually add the egg mixture in a slow, steady stream into the hot cream in the saucepan. Cook over low heat, stirring occasionally, until the custard thickens enough to coat the back of a spoon and reaches 170 degrees on an instant-read thermometer, about 6 minutes.
Remove from the heat and strain into a large bowl. Add pistachio mixture and almond extract. Cover with plastic wrap, pressing down against the surface to keep a skin from forming, and chill in the refrigerator for at least 2 hours.
Remove from the refrigerator and pour into the bowl of an ice cream machine. Freeze according to the manufacturer's instructions. After the ice cream is made, transfer to an airtight container and freeze until ready to serve.
Garnish with whipped cream and toasted pistachios.