Preheat your oven to 350F and grease and line the bottom of the pan with parchment paper.
Process the pistachios with the potato starch until fine.
Measure the flour, baking powder, baking soda and pistachio mixture and set aside.
Cream the butter with the sugars until light a fluffy, about 4-5 minutes if using a stand mixer fitted with the paddles attachment. Or, 2-3 if using an electric hand mixer.
Scrape the bottom and sides of the bowl then add the eggs with the mixer on high speed one egg at a time.
Reduce mixer speed to low, then add the flour mixture in three parts alternating with the sour cream in two additions. Mix in the last portion of the flour using a rubber spatula.
Spread the batter into the prepared pan and bake over the middle oven rack for 35-38 minutes, util the cake is puffed, golden brown and when a toothpick comes out clean from the center of the cake.
Remove from the oven and allow the cake to cool in the pan for about 20-30 minutes, then run a knife between the cake and the pan then turn it over to your serving plate.