Preheat the oven to 325F (160C), grease the bottom of one nine-inch pan, and line with parchment paper.
Sift the flour, potato starch, and baking powder in a medium bowl.
In a bowl of a standing mixer fitted with the paddle attachment, beat the sugar, zest and butter on medium-high speed until light and fluffy, about 4-5 minutes.Scrape the bottom and sides of the bowl 2-3 times during the mixing time. With the mixer on medium-high speed, add the eggs, one at a time, waiting for each egg to fully incorporate before adding the next. Scrape the bottom and sides of the bowl between each addition.
Mix in the vanilla bean paste.
Stop the mixer, sift the dry ingredients over the butter and egg mixture, then mix on low to fully incorporate.
Use a rubber spatula to scrape the bottom of the bowl and make sure there are no unmixed eggs and flour, then evenly spread the batter into the prepared pan.
Bake for 40-45 minutes until the top of the cake is golden brown and a toothpick comes out dry from the center of the cake. A few moist crumbs are ok.
Remove from the oven and let the cake cool completely on the pan before inverting it to your serving plate.
Dust with powdered sugar, and serve.