Use a large knife to cut the kernels from the corn cobs. Place in a large pot, or Dutch oven.
Break the corn cobs in half and add to the pot, along with the milk, cream and 1/2 cup of sugar.
Bring to a boil, stirring occasionally, then remove from heat and let stand for 1 hour to infuse the flavors. Then, discard the cobs.
Puree the kernel mixture in a blender.
Add back to a saute pan and bring to a simmer, then turn off the heat
In a medium bowl, whisk egg yolks, 1/4 teaspoon salt, and 1/4 cup of sugar.
Add a cup of the hot cream mixture to the yolks, stirring constantly.
Add yolk mixture to saucepan, stirring. Cook over medium-low heat, continuing to stir constantly, until custard coats the back of a spoon - about 10 minutes.
Pass the custard through a fine sieve, pressing the solids. Discard solids.
Whisk in sour cream until smooth.
Let custard cool in an ice bath, then cover and chill for at least 4 hours.
Freeze corn mixture in your ice cream maker according to the manufacturer's directions.
Add the pistachios 5 minutes before the churning is to finish.
Place in freezer-proof container, and freeze for 1 to 2 hours, or overnight.